US AAC/AAF Doctrine: FM 1-10, Air Attack, 1940 - 4. Air Attack Planning and Operations
CHAPTER 4: AIR ATTACK PLANNING AND OPERATIONS
SECTION I - PLANS AND PLANNING
117. GENERAL.-This chapter includes a discussion of technique applicable to the successful accomplishment of the assault phase of the bombardment mission. The technique of air attack must be suited to the conditions under which the mission is performed in order to insure the most effective utilization of the force employed and to minimize the losses resulting from enemy opposition. The method best suited for use in any particular situation can be determined only after consideration of the factors affecting the success of the mission.
118. PLANS.-Plans for bombardment operations can be formulated only after due consideration of all probable and possible contingencies which may arise during the conduct of the mission. By such planning the possibility of encountering unforeseen circumstances is reduced to a minimum. Thorough understanding of the plan of the combat commander by all elements of the command is important to the successful accomplishment of bombardment missions. It is desirable that plans of operations are given in requisite detail for all phases not covered by indoctrination; also that they are as simple as the situation permits.
119. ALTERNATIVE PLANS.--a. Plans should be prepared for attacks against alternate objectives when targets cannot be attacked in the order of priority established in combat orders. A commander may be unable to operate against objectives in the order of their assigned priority because of adverse weather or other conditions which would expose his command to unjustifiable risks not foreseen by the higher commander. In such a case, the combat commander is justified in the attack of objectives of a lower priority. These will normally be secondary objectives which, because of their being undefended or lightly defended, require no complex scheme of maneuver for their attack.
b. When a combat commander while proceeding on another mission unexpectedly gains contact with a fleeting objective not covered by instructions, he must use his initiative and judgment in deciding the proper course of action. In reaching a decision, he must consider the nature and importance of his mission, security of his command, importance of the fleeting objective, the likelihood of its destruction by other forces, and adequacy of the fire that he is able to deliver.
120. INFORMATION REQUIRED.-The effectiveness of the operations plan is largely dependent upon the completeness and accuracy of the information available. Information pertinent to the planning of bombardment operations may be considered under three categories: information of the objectives; information of the enemy activities; and information of pertinent weather conditions.
121. INFORMATION OF OBJECTIVES.-Much information of fixed objectives will be obtainable initially from pertinent objective folders which normally are made available to the commander charged with the preparation of plans for air attack missions. Information of transient objectives will be accumulated and filed in objective folders after the commencement of active operations. In many situations the available information of fleeting objectives will not be sufficient for the preparation of complete plans for their attack. In such situations, indoctrination and training must be depended upon to exploit favorable opportunities for effective operations against the fleeting objectives.
122. ASSIGNMENT OF OBJECTIVES.-Objectives for air attack are assigned in combat orders. Orders assigning objectives in the order of their importance will establish an operating priority. Whenever possible, a sufficient number of objectives should be assigned to each unit to permit the selection of alternate targets in the event that unforeseen conditions prevent the attack of objectives in the order established in the operating priority. Fleeting objectives when given precedence over other assigned objectives should be designated in relative order of importance.
123. INITIATIVE.-The bombardment commander, by selecting a time of attack and altitude which are least favorable to the defender, can gain an initial advantage. The defender cannot be equally strong on all points; hence, a wise selection of bombardment objectives, in conjunction with the most advantageous times and altitudes at which to deliver the assault, is an important factor in the successful penetration of antiaircraft defenses. However, once hostile pursuit effects interception, the initiative passes. The action of the enemy will determine the time to engage and withdraw as well as the direction and number of assaults.
124. NATURE OF TARGETS.-A target is the space within which fire must be placed to accomplish the desired result. The objective and the target are one and the same when the entire objective is vulnerable and direct hits are required. The target may be larger than the objective if hits nearby are effective, smaller if hits are effective only on certain parts of the objective. An airdrome is an example of an area target; a bridge, that of a point target.
125. INFORMATION OF ENEMY.-It is important that all possible information be available of the location, strength, and composition of such enemy forces as may affect the conduct of the mission. Knowledge of the performance characteristics of hostile fighting aircraft and of the enemy's air fighting tactics is an important factor of information. The objectives of bombardment attacks frequently will be located deep in enemy territory, and all hostile forces which may be encountered, whether en route or in the vicinity of the objective, must be considered when plans for the attack are prepared. In planning a bombardment attack, every effort must be made to avoid exposing the command to unnecessary risk of hostile interference.
126. INFLUENCE OF WEATHER CONDITIONS.-a. Weather conditions should be regarded not only as possible obstacles to be overcome in the conduct of a mission or of an air offensive, but also as a varying situation the most favorable aspects of which should be selected to render the maximum assistance to the attacking force. From this point of view there are three general uses of weather advices:
(1) When an air offensive is being planned, summaries of climatic conditions in the theater of operations should be consulted by the planning agency to ascertain the probable weather in which operations will have to be conducted, and to plan, in general, the method of operation which will utilize to a maximum the favorable aspects of such weather conditions. At this phase of the planning, expected weather conditions will influence the choice of aircraft employed, location of operating bases, frequency of contemplated missions, and other general factors.
(2) Higher commanders will require forecasts of weather conditions over definite areas and routes for periods up to 36 or 48 hours in advance of the issuance of orders for specific missions.
(3) Shorter range forecasts should be made available for subordinate commanders. Detailed plans for the missions should be prepared in accordance with expected weather conditions. Furthermore, the air leaders should be so thoroughly conversant not only with expected weather developments, but also with the possible variations therefrom that may occur, that plans may be intelligently modified in the air, in order to utilize to the maximum the assistance available from the weather situations existent during the period of conduct of the mission. Details of the commander's plan, influenced by weather conditions, include the determination of the force required for the mission, time of attack or assembly, routes and formation to be flown, method, altitude, and axis of attack, need for a rally, and selection of secondary objectives.
b. Even with the most careful consideration of the influence of weather conditions on the conduct of the attack, completely unanticipated weather situations may arise, necessitating changes in the manner of performance of the mission. Through indoctrination and training of all echelons, tactical units must be prepared to take appropriate action in unpredictable situations.
127. COMMUNICATION.-The manner and effectiveness of tactical control of the combat command depend to a considerable extent upon the nature and reliability of the means of communication employed. Adequate means of communication are essential in operations involving tactical control during the conduct of a bombardment mission, and this factor must be carefully considered when plans are formulated. The use of radio, particularly when deep in enemy territory, may disclose the position of the combat command; hence the employment of this means of communication should be held to a minimum when there is danger of facilitating interception by hostile aircraft.
128. ATTACKING FORCE.-The plan of operations must not call for the accomplishments of results which are beyond the capabilities of the force available. The size of the force required to accomplish a particular mission depends upon the requirements of the mission, skill and training of available tactical units, and nature and effectiveness of hostile antiaircraft defense measures. The size of the force to be employed is left to the judgment of the combat commander whenever practicable.
129. CONCURRENT AIR OPERATIONS.-Team play and coordination are essential to the attainment of maximum results in the conduct of bombardment operations. It is important that all of the air activities in the air theater of operations be so coordinated that the bombardment operations, as a whole, properly fit into the general plan of employment for the aviation forces. The best results cannot be expected from an uncoordinated aggregate of unrelated assaults, even though each such assault may have gained a measure of success in its own locality. When several important objectives or groups of objectives are to be attacked, a considerable degree of security for the attacking forces may be gained by having separate air attack operations conducted concurrently. Security from the hostile air fighting forces is obtained by this simultaneous employment, because it is impossible for the defender to engage the attacker simultaneously at every point with his full strength.
130. COORDINATION OF SUPPORT.--a. (1) The supported unit is the basis for the establishment of coordination in bombardment operations. The details necessary for securing coordination of the supporting operations should, whenever practicable, be left to the commander of the supported force. When coordinating details are prescribed by higher authority, the nature of such details is determined primarily by the ability of the supported force to meet the requirements thus imposed. Higher authority may make provision for coordination of the support by the following methods:
(a) Attachment of supporting units.
(b) Designation of supporting units and their general missions; prescribing necessary measures for coordination; or directing the supported command to prescribe the additional details required.
(c) Organization of task forces for a series of coordinated missions.
(2) The time of attack is not designated by higher authority for the purpose of securing coordination, unless no other means of effecting coordination is practicable.
b. The commander of the supported force normally issues necessary instructions to such supporting units as are attached to his command. The instructions include such details of the plan of action as are necessary to secure coordinated support and are issued in time to permit proper planning by the supporting units. The commander avoids committing himself to an inflexible plan of action unless such a course is definitely warranted by the situation.
c. When a time of attack is specified for the purpose of effecting coordination of the support, the time usually is selected by the commander of the supported force either before take-off or as soon as possible during the advance to the initial point. The time of attack should be selected as early as practicable, but not before it becomes apparent that the announced time is practicable.
d. When the operation involves a supporting attack and the time of attack is to be determined after take-off, the support force assembles with and guides on the supported force, keeping within such distance as will assure the continuous maintenance of signal communication. When the time of attack has been signaled, the supporting force takes such action as is required to protect the attacking force during the assault. When the time of attack is announced before take-off and assembly with the supported force is not practicable or desirable, the commander of the supporting force selects his routes and conducts the mission in a manner that will insure the protection of the supported force during the assault.
e. When the advance only is made during darkness, the supporting force assembles with the supported force at dawn, when practicable, in order to insure coordination at the objective. When the attack is made during darkness, the time of attack must be announced before take-off, unless conditions permit maintenance of signal communication, accurate navigation, and fixation of position during the advance. When required, coordination of supporting operations at night usually can be effected by both supported and supporting forces working by a predetermined time schedule.
f. The attacking force furnishes such auxiliary support of its own operations as is consistent with the effective utilization of the force. When auxiliary support is furnished for guidance during the advance or for illumination of the objective, the commander of the supported force prescribes all details that are essential for coordination.
SECTION II -BOMBING PROBABILITIES
131. GENERAL.-The bombardment commander, in order to utilize his force most effectively, requires information which will enable him to estimate the minimum force required for the accomplishment of any particular bombardment task. The accuracy of aerial bombing is affected by a great many factors, the more important of which must be taken into account in the solution of problems in bombing probabilities. Bombing probabilities are not susceptible of exact mathematical determination. Tables are available, however, whereby a bombardment commander may, by the application of his knowledge of the performance of his particular organization, estimate the requirements for the successful accomplishment of bombardment missions. Such tables, together with type problems illustrating their use, are included in this section.
132. HITS REQUIRED.-After selection of the proper size of bomb to use against a particular objective, it is necessary to determine the number of hits required to produce the desired degree of destruction. The information furnished in the objective folder should be adequate for this purpose. A large proportion of individual bombardment objectives may be destroyed if hit by one properly selected size of bomb. Objectives including numerous structures or elements may sometimes be appropriately divided and so assigned that if each element is hit by one bomb of proper size its destruction will be complete. Certain structures or facilities may require a number of hits, all of which must be sighted at a single aiming point or target. Still others will require a uniform pattern of hits over a given area. These factors must be considered in the planning to determine the number of effectively placed bombs required to complete the mission with the required degree of assurance of success.
133. SIZE OF FORCE.-It is necessary to determine the size of the force which must be employed on the mission to assure a reasonable chance of obtaining the required number of hits under the prevailing conditions. Economy of force dictates the dispatch of the smallest practicable number of air-planes. On the other hand, the chance of successfully accomplishing the assigned mission increases with the size of the force dispatched, and this consideration indicates the dispatch of ample force. The effect of antiaircraft opposition, obviously, will not be accurately predictable at the beginning of any war nor at the beginning of any missions. Any factor applied to allow for action of the enemy should be applied after a careful estimate of the strength required at the bomb release line based upon the characteristics of the target and upon the established record of probable errors of the units which are to do the bombing. These are tangible factors and when properly deduced should be employed to the fullest extent. The invariable use of his entire force by a commander, whatever the mission assigned, in order to be most certain of success is normally unsound.
134. SKILL OF PERSONNEL.-The skill of bombardment personnel can best be ascertained from the recorded results attained by them in bombing practice. It is important that bombardment commanders, particularly squadron and group commanders, have accurate records of the results attained by their bombing teams under various conditions of practice simulating, as nearly as practicable, the conditions expected to be encountered during war. Such records provide the best means of estimating the accuracy factor to be applied in the determination of bombing probabilities.
135. BOMBING ERRORS.-a. Errors in bombing as used for measuring results and for making predictions of future results are defined as the distances by which bombs (or the mean point of impact of patterns of bombs) miss the center of the target at which they are aimed. The range error is measured parallel to the direction of the bombing approach; the deflection error, perpendicular to the direction of approach; and the circular error is measured on a radial straight line connecting the point of impact with the center of the target.
b. Errors in bombing result from many causes, some determinate, many indeterminate in extent. Some errors are systematic in nature, others accidental. For purposes of study to improve bombing accuracy, the extent and sources of systematic errors are sought in order to remove their several causes, whether said causes are defects of instruments, equipment, data, technique, training, or other source of inaccuracy.
136. AVERAGE ERRORS.-a. Tables of average errors are the foundation upon which predictions can be calculated for the success of operations under similar conditions. The process which is involved in the determination of the probabilities of success, or of a certain percentage degree of success of a given mission, except for the tables of average errors (and aside from antiaircraft opposition), is mathematically sound.
b. The smaller the average error of a given individual bombardier, bombing team, or organization, the greater will be the chance of success on a bombing mission similar in nature to the type on which that small average error was attained. Average errors are of little value unless the number of releases which enter into those averages is relatively large and each is properly evaluated. All results of the droppings of bombs cannot be grouped into one single set of figures to form a single average. Experience has shown the necessity of separate averages of errors for bombing at the several different altitudes used by bombardment aviation. It has been found, therefore, to be a necessary step in the proper training of individuals, bombing teams, and organizations to maintain tables of average errors for each such individual, bombing team, or unit for various bombing altitudes.
c. The results of each practice, after analysis, should be added to the cumulative result of previous similar practices. Analysis of each practice is necessary in order that errors may be properly evaluated in accordance with conditions. It is appropriate in the establishment of averages of this type to discard or eliminate from the summation a proportion of the earlier data accumulated. This may occur because earlier data have become inconsistent with the results obtained after more thorough or advanced training, or those attained by the use of more modern or accurate equipment. This can probably best be done on an annual training year basis and should be done only as prescribed from time to time.
d. An organization commander should be able at any time to make a relatively correct estimate of the results of bombardment missions of a given type to be expected by any bombing team, or element of his organization, through calculations based upon properly maintained tables of average errors for all conditions for which such predictions may be necessary.
137. PROBABLE ERRORS IN BOMBING.-Probable errors as used in connection with probabilities of hits in bombing are those errors which are as apt to be exceeded as not. Probable error has a simple arithmetic relation to the average error obtained under a given set of conditions by a given individual. The relationship gives an approximate value of probable error that is close to the correct value if the average error used is based upon a reasonable number (50 or more) of releases made under the given set of conditions.
138. RELATIONSHIP OF PROBABLE ERRORS TO AVERAGE ERROR.
a. Having the recorded average errors of his command, the commander can prepare a table of probable errors for his unit by the application of the following mathematical relationship between probable errors and average errors:
Range probable error (Rep) =0.845 times the arithmetic mean range error (0.845 Rea).
Deflection probable error (Dep) =0.845 times the arithmetic mean deflection error (0.845 Dea).
Circular probable error (Cep) =0.939 times the arithmetic means circular error (0.939 Cea).
b. The probable errors shown in table V are representative of results actually attained in the dropping of a large number of bombs. These values are included for convenience in solving illustrative problems and are not necessarily representative of either present or expected future bombing results.
c. Probable errors for use in planning bombardment missions should be computed from results actually obtained by the bombing team or unit in question under comparable conditions of bombing. No single table of probable errors is suitable for use under all possible conditions of bombing.
139. VULNERABILITY FACTORS.-a. The probable errors of individual teams or bombardment units are best expressed in feet and are measured from the center of the target. The likelihood of hitting a particular target depends upon the probable error and the size of the target. Thus, if the range dimension of a target is equal to twice the probable error in range, and the range error of the point of impact of a given bomb does not exceed its probable error either short or over, then a hit, as far as range is concerned, is obtained within the vulnerable limits of either the near or far half of the target. The same reasoning applies to a hit, as far as deflection is concerned.
b. (1) Figure 10 shows the relation of target dimensions to probable errors and the physical meaning and application of the term "probability factor."
(2) The target is represented by the rectangle ABCD, any part of which is vulnerable. BC is the vulnerable dimension in the range direction, and AB is the vulnerable dimension in the deflection direction. Hence BF is one half the vulnerable range dimension, 1/2 RDT; and EB is one half the vulnerable deflection dimension of the target, 1/2 DDT, BF and EB are the allowable errors, the errors to either side of the aiming point which cannot be exceeded without missing the target.
TABLE V. Probable errors
(3) The values NT and SN are, respectively, the range (Rep) and deflection (Dep) probable errors. The strip between MN and PO, if extended to infinity both to right and left, would contain one half of the bombs dropped. The strip between MP and NO if similarly extended would also contain one half of the bombs dropped.
(4) If BF and NT are equal, that is to say if one half the range dimension (1/2 RDT) of the target equals the probable error, any bomb dropped has a 50-50 chance of hitting the target insofar as range is concerned. It is obvious that if the value of BF is greater than that of NT there is a greater than 50 percent degree of certainty of hits as far as range is concerned. Since BF and NT are seldom equal it is necessary to provide a means of evaluating the chance of hitting the target for any ratio of those values. The ratio of those values is called the vulnerability factor for range. Similarly the ratio EB to SN is the vulnerability factor for deflection.
c. (1) Thus the vulnerability factor in range equals one half the range dimension of the target divided by the probable error in range:
Vulnerability factor in range = 
in which RDT represents the range dimension of the vulnerable part of the target.
(2) The vulnerability factor in deflection equals one half the deflection dimension of the target divided by the probable error in deflection:
Vulnerability factor in deflection = 
in which DDT represents the deflection dimension of the vulnerable part of the target.
d. Similarly, the vulnerability factor for circular targets equals the radius of the vulnerable part of the target divided by the circular (or radial) probable error:
Circular Vulnerability factor = 
in which RCT represents the radius of the vulnerable portion of the circular target.
140. PROBABILITIES OF HITS.-Corresponding to each deflection or range vulnerability factor there is a percentage of chance of a hit insofar as that direction is concerned. When using rectangular errors, separate probabilities must be found for a hit with respect to range and for a hit with respect to deflection. The product of those two values gives the probability of the concurrences of the two events - thus, of a hit on the target. When using circular errors and circular targets, a single value - which is the probability of a hit on the target-may be ascertained from the single ratio, the circular vulnerability factor.
FIGURE 10.-Relation of target dimensions to probable errors.
141. VULNERABILITY FACTORS AND PROBABILITIES.-Probabilities corresponding to known vulnerability factors up to a value of 6 are contained in tabular form in table VI and in graph form in chart No. 1. Having determined the vulnerability factor pertinent to the conditions under which bombing is to be done, the probability of the independent event of a hit in range or in deflection may be read off directly from either table VI or the curve of chart No. 1.
142. SINGLE SHOT PROBABILITY.-The probabilities determined from table VI or from chart No. 1, as described in paragraph 141, are, respectively, the range single shot probability (RSSP) and the deflection single shot probability (DSSP) of hits with respect to those axes of the target, separately considered. The combined (range and deflection) single shot probability (SSP) is the product of RSSP multiplied by DSSP. A hit by a single shot is not possible except by the concurrence of the two events, a hit in range and a hit in deflection. For convenience and simplicity the "combined range and deflection single shot probability of a hit" will hereafter be referred to as the "single shot probability." The single shot probability of a hit on a circular target, using a known vulnerability factor, may be read directly on the curve of chart No. 2.
143. BOMBS REQUIRED.-The single shot probability (SSP), determined as outlined above, is the basis for the calculation of the number of individually sighted (or aimed) bombs required to provide a certain percentage degree of assurance of securing one hit and/or the number of bombs required to provide a certain percentage degree of assurance of securing at least a given number of hits. The SSP does not indicate the percentage of hits to be expected from a given number of bombs. Curves showing the number of bombs required to give a predetermined chance (50 percent-99.5 percent) of one or more hits under various conditions of bombing are contained in chart No. 3. Charts Nos. 4 to 9, inclusive, show the number of individually sighted and released bombs required for a predetermined chance (50 percent-99.5 percent) of securing one or more, two or more, and up to ten or more hits. The percentage chance of obtaining at least one hit with from 1 to 10 bombs can be read directly from the curve of chart No. 10.
144. TRAIN BOMBING PROBABILITIES.-a. General.-Train bombing is the release of two or more bombs in succession from the same airplane by a single sighting operation with an exact interval between the bombs. The important feature is that the distance between adjacent points of impact must be less than the vulnerable range dimension of the target in order not to bracket the target with any two adjacent bombs. This is accomplished by setting the calculated time interval on the release mechanism and should be obtained within the limits of average errors due to ballistic and other causes.
b. Line of attack.-The direction of approach and the line of attack or ground track of the airplane during the final part of approach and bomb release should be selected to assure the greatest probability of a hit, other conditions permitting. The sighting operation should attempt to put the center of impact of the bomb train on the center of the target. In the selection of the line of attack, the following points should be considered:
(1) The allowable error in range equals one half the vulnerable range dimension of the target plus one half the length of the bomb train.
(2) The range probable error of the center of impact of the train is the same as for an individually sighted bomb and should be so used in calculations.
(3) The probable error in deflection is the same as for an individually sighted bomb.
(4) The relative values of range and deflection probable errors of the particular bombing team will influence the direction of approach to elongated objectives. (See par. 189.)
c. Probability of hit.-Taking advantage of the fact that the allowable error in range is increased by one half the length of the train, the smaller dimension may be used as the range direction with a consequent greater increase in the probability of a hit than if this smaller dimension was used as the deflection dimension. Calculations of the probability of a hit by a single train should be made as explained above for an individually sighted and released bomb. The center of impact of the train should be considered as though it was the point of impact of a single bomb and increasing the allowable range error by one half the length of the train in the calculation. This, of course, will be the probability of a single hit by the train if the spacing between bombs is equal to or only slightly less than the vulnerable range dimension of the target.
145. FORMATION OR PATTERN BOMBING PROBABILITIES.--a.General.-(1) A maneuvering target which makes a material change of speed or direction during the time of fall of a bomb will not be hit (except by chance) by a bomb which is accurately aimed at that target and released from a high altitude. Unless it is possible to predict those changes, the target cannot be expected to be hit, from high altitude, by an accurately aimed and delivered single bomb. Against such targets pattern bombing may be necessary. Against stationary targets such as railroad yards, oil tank farms, and, in some cases, airdromes, it is desired to place a great number of bombs with uniform distribution within a certain area. Point targets may be bombed from formation when the action of hostile pursuit aviation demands it. Many combinations may be used, and experience, practice, and established records of results must be depended upon to assist a commander in his decision as to how best to meet each condition.
(2) Bombs can be released individually or in train at varying time intervals. Airplanes may be flown individually or in large or small formations. The formations may be echeloned in depth, width, or altitude. The numerous combinations of these factors are sufficient to fit any pattern to any target. Only training and practice within each unit can determine which of these combinations is best suited to the several types of targets requiring pattern bombing, and the reliability with which a given pattern may be produced and duplicated by the tactical unit. The method of establishing reliability with which a given pattern may be produced and of placement is similar to the method of establishing reliable individual average errors.
b. Probability of hits.-(1) General.-The use of pattern dimensions to increase the allowable error of placement of the center of impact presupposes that the unit has had sufficient training and practice to have established reasonably reliable "average dimensions" for that type of pattern.
(2) Area pattern probabilities.-(a) The probability that any one bombing formation volley will result in geometric, uniform distribution is remote. It is equally true that distribution approaches geometric uniformity as the number of volleys dropped on a target approaches infinity. There are no available data from which to determine the probability of "holes" in the pattern occurring in any one volley. Reliable results from training and practice must be depended upon to provide a measure of pattern size, shape, density, uniformity, and the degree of accuracy of placement thereof.
(b) Training and practice should include the several types of formations with various adjustments as to intervals and distances between airplanes, and with individual and train , releases from each airplane. Types of sighting operation should include principal sighting operation by the leading bombing team, other bombardiers releasing on their own range sightings. Some method should be practiced involving a plan of convergence of airplanes while approaching the bomb release line, in such manner that each bombing team can perform its own complete sighting operation.
(3) Train bombing from formation.-The pattern produced by train release from a single airplane may not be sufficiently wide to secure a required probability of a hit on a point target. It may be desirable for tactical reasons to meet this requirement by use of several airplanes in formation, particularly to widen the pattern. Increased intervals between airplanes in formation or more airplanes may be used to widen the pattern within limits and with due caution against "holes" in the pattern. In calculating the probability of a hit, the allowable errors may be increased by one half the average dimensions, in range and deflection, of type patterns for which reliable averages have been attained by the unit.
(4) Density of pattern.-The density or number of points of impact per unit area, within the pattern produced by single bombs released simultaneously by the airplanes of a formation (bombing formation volley) , may be increased by closing the formation to a more compact one, or by increasing the number of bombs to be released, in train within a given time from each airplane of the formation. The probabilities of covering a target with a pattern are obviously greater when the size of the pattern is increased. The practical limitations of decreased density, probable lack of uniformity, or excessive numbers of bombs required must be balanced against the advantages of increased size of the pattern.
146. BOMBING PROBABILITY CALCULATIONS.-The calculations of bombing probabilities in accordance with the mathematical law of errors is a long and tedious task if a broad scope of conditions is to be covered. The curves shown on charts Nos. 3 to 9, inclusive, enable the bombardment commander to solve a wide variety of bombing problems with a minimum of mathematical computations. Having a knowledge of the capabilities of his unit and information of the objective and of the conditions under which the bombing is to be accomplished, he can then complete his solution by means of the curves on those charts.
147. ILLUSTRATIVE PROBLEMS.-There are included here four typical bombing problems and their solutions. Familiarity with the use of the curves in the solution of problems can be acquired from a study of these problems. Additional problems should be devised and solved as a matter of training.
148. PROBLEM No. 1.-a. Factors.-It is urgent that a very important building be destroyed. The bombardment commander is ordered to destroy the objective with the least possible delay. His objective folder and other sources of data contain the information that the objective is 800 feet long and 300 feet wide; that it is defended by antiaircraft machine guns and 37-mm caliber cannon; that 100-pound bombs with delay fuzes will destroy the objective; and that eight direct hits are required for complete destruction.
b. Decision as to required chance of success.-He decides that the urgency of the situation and other tactical considerations demand that he take no less than 90 percent chance of success of accomplishing his mission in one operation.
c. Decision as to altitude.-The effectiveness of the anti-aircraft defense of this particular target and other considerations cause him to decide that he will bomb from no lower than 8,000 feet.
d. Decision as to target dimensions.-His target in this case is the objective itself. He is required to obtain direct hits. Bombs striking within a few feet alongside the building may undermine walls, but the danger radius of these small bombs is so short that the dimensions of the target are substantially the same as the dimensions of the objective, i. e., 800 by 300 feet.
e. Decision as to direction of approach.-The directive from higher authority did not specify direction of approach. Study of objective folder indicates no controlling factor such as known or expected location of batteries of the antiaircraft defense guns. The commander considers the probable errors of his unit in range and deflection. Assume these to be as shown in table V. The range probable error is the smaller so his decision is to approach the bomb release line on a direction parallel to the shorter target dimension.
(For solution, see par. 152.)
149. PROBLEM No. 2.—A bombardment group commander is directed to attack and destroy section of a canal lock structure. Details of its location and antiaircraft defenses are furnished. Vulnerable dimensions are 100 by 800 feet. A direct hit is required. On the basis of the directive and study of the details furnished, the commander makes the following decisions and applies them to a solution of the force required:
a. Degree of certainty of one or more hits-90 percent.
b. Altitude to be used-16,000 feet.
c. Size of bomb to be used-2,000-pound.
d. Number of hits required-one.
e. To attack the structure at approximately 90° to its long dimension.
f. To drop one individually sighted bomb by each airplane on its arrival at the bomb release line.
(For solution, see par. 152.)
150. PROBLEM No. 3.-a. A bombardment group commander is directed to attack and destroy an enemy light cruiser which is being used as a commerce raider. The dimensions of the vulnerable area of the objective, including danger radius at sides and stern (table IV), are 130 feet in width and 610 feet in length. The target is free to maneuver. It has normal antiaircraft artillery.
b. It will be attacked in the manner indicated by figure 15. The force required will be estimated on the basis of formations (flights of three planes each) required if attack is along the axis of travel of the target considering no maneuver on the part of the target. Right and left wing flights will then be added to guard against failure of the mission because of target maneuver.
c. Four 600-pound bombs will be carried by each airplane. Bombs of each airplane will be released in train with spacing of 100 feet between adjacent bombs. The pattern width for each flight is 150 feet.
(For solution, see par. 152.)
151. PROBLEM No. 4.-a. A bombardment group commander has been given the mission of destroying a bridge which is vital to the communication of the enemy. Heavy troop movements are in progress over the bridge. It is now defended by antiaircraft machine guns and there is some pursuit aviation defense of the area including the bridge. Antiaircraft artillery cannot be expected to be installed for about 24 hours. Details of the bridge are furnished and indicate the critical point of attack to be a pier whose vulnerable dimensions are 50 by 50 feet. These dimensions include the danger radius in all directions with respect to the pier and a vital part of the structure adjacent to the pier. One hit with a 600-pound bomb within the vital area will suffice to destroy the usefulness of the bridge.
b. On the basis of the directive and study of the details furnished, the commander makes the following decisions in the solution of the force required:
(1) Degree of certainty of one or more hits-90 percent.
(2) Altitude to be used-6,000 feet.
(3) Size of bomb to be used-600-pound.
(4) Number of hits required-one.
(5) To attack the structure in a direction perpendicular to the direction of the bridge at the pier.
(6) To attack with a formation of whatever size required in order to provide defense against probable pursuit interference.
(7) To require bombing team in leading airplane to direct the approach to the target.
(8) To specify the order in which other bombing teams will take the lead in case of casualties to leaders. All bombardiers to drop their bombs on their own range sighting.
(9) In order to limit the number of approaches to the target to one, each bombardier is to release 6 bombs in train, with a time interval to give 40 feet between adjacent points of impact.
c. From training and practice the commander has the following information regarding the capabilities of his bombing teams and units:
(1) Average range probable errors are as in table V.
(2) Average deflection probable errors are as in table V.
(3) Average pattern width, stagger formation (squadron), with uniform distribution is here considered to be 320 feet.
(4) Bombardier and bombing team average errors are substantially the same, and each is fully capable of directing the approach of the formation to the target.
(For solution, see par. 152.)
152. SOLUTIONS OF PROBLEMS.-The solutions of illustrative problems Nos. 1 to 4, inclusive, itemized and tabulated for convenience of reference, are included in table VII.
TABLE VII
153. RESULTS.-a. Problem No, 1. The bombardment commander finds that he must be prepared to drop not less than 10 bombs to be assured a 90 percent probability of securing the 8 hits required to accomplish this mission.
b. Problem No. 2.-The commander finds it necessary to drop 13 bombs under the conditions imposed. (It should be noted in connection with this illustration that a 50 percent probability of at least 1 hit could be attained with 4 bombs.)
c. Problem No. 3.-The commander finds it necessary to use 5 patterns using trains of 4 bombs from each of 3 airplanes or a total of 60 bombs. If bombs of both right and left wing flights are dropped because of target maneuver the total bombs expended will be 180.
d. Problem No. 4.-The commander finds it necessary to use (1.5 or) 2 patterns. Thus 2 squadrons of 9 planes each, releasing 6 bombs in train from each airplane, a total of 108 bombs, will provide a 96 percent chance of 1 hit. (See chart No. 10 - Appendix - , on which a single shot probability of .791 shows a 96 percent chance with 2 bombs (patterns). One pattern (54 bombs) provides an 80 percent chance of the one hit required.)
154. ANTIAIRCRAFT OPPOSITION.-The above solutions indicate the numerical requirements in bombs and force to accomplish the missions stated if done under conditions comparable to those under which performance data (probable errors) used were determined. It is at this point in the solution that the judgment of the commander must be applied in estimating the probable effect of hostile antiaircraft measures and the extent to which his force should be augmented to accomplish the mission as planned despite anticipated losses.
SECTION III: MINIMUM ALTITUDE ATTACKS
155. NATURE OF OPERATIONS.-The performance of minimum altitude attacks requires a highly maneuverable airplane, and, in general, only light bombardment and pursuit units engage in this manner of operations. The objectives of minimum altitude attacks frequently are targets of opportunity against which surprise is an important factor in obtaining the most effective results. Minimum altitude attacks habitually are performed at the lowest altitude consistent with security requirements at which it is feasible to operate the aircraft employed. Aircraft intended for use in such operations normally are equipped with forward firing fixed machine guns for the provision of protective covering fire against the defensive fire of hostile ground weapons.
156. BOMBING RELEASES.-Minimum altitude attacks normally are conducted without the use of a precision sight. The release of bombs in train is normal. Release intervals are regulated to provide a bomb spacing which will not be wasteful of bombs and yet insure a continuous danger area throughout the length of the train.
157. MUNITIONS.-The selection of type of fire depends upon the nature of the objective and whether the purpose of the mission is to destroy or to neutralize it. The munitions usually employed in minimum altitude attacks are demolition bombs, fragmentation bombs, chemical bombs, and other chemical agents.
158. MANNER OF ASSAULT.-Minimum altitude attacks usually are accomplished, particularly when surprise can be effected, by aircraft making a single assault. The group is the largest combat command employed on minimum altitude missions. The combat command may be divided into smaller units, each of which is assigned a specific objective or portion of a large area target, whenever the circumstances require such action. Small targets which are clearly visible are most effectively attacked by airplanes assaulting singly. In the presence of hostile pursuit it may be necessary to employ either 3, 6, or 9 airplane assault units in order to provide adequate concentration of defensive fire. The attack of objectives defended by antiaircraft ground weapons is accomplished in one approach by each assault unit whenever practicable.
159. TIME of ATTACK.-Minimum altitude attacks may be performed either at night or during daylight. Targets of opportunity, incident to enemy troop movements, frequently will exist only during the hours of darkness. The time of attack should, whenever practicable, favor the attacker and surprise the enemy. When the minimum altitude attack is in support of a primary high altitude mission, close cooperation and accurate timing are essential to the most effective results. Liaison with the supported force is maintained by radio whenever practicable, otherwise by a time schedule.
160. DIRECTION OF APPROACH.-The direction of approach is an important factor in the success of minimum altitude attacks. The position of the sun or moon, the terrain in the vicinity of the objective, the nature and extent of the target, also the location, composition, and strength of antiaircraft defense forces, are important factors in determining the most advantageous direction of approach. A down-wind approach facilitates surprise and minimizes the exposure of assault units to antiaircraft fire.
161. AREA TARGETS.-Large areas such as cantonments, bivouac or entraining areas, large transportation parks, rail-way yards, or airdromes usually are attacked in formation by releasing bombs in trail or spraying chemicals. Large areas, particularly when strongly defended, should be attacked by a force of sufficient strength to cover the entire area in one assault. Large area targets are divided into portions, each of which is assigned as the objective of a separate assault unit.
162. LINEAR TARGETS.-Long narrow targets such as troop columns, railway trains, railway tracks, or truck trains are best attacked by small assault units of from one to three airplanes, depending upon the width of the area to be effectively covered. When the objective is defended the assault units approach and depart obliquely, flying in prolongation of their target only during the actual delivery of fire. Very long targets are divided into sections, each of which is assaulted by a separate unit. Assaults are made simultaneously when practicable.
163. NEUTRALIZATION OF ANTIAIRCRAFT ARTILLERY DEFENSES.-a. Bombardment operations against strongly defended objectives frequently can be given effective support by minimum altitude attacks for the purpose of interfering with or neutralizing the antiaircraft artillery defenses. The attack of such objectives at minimum altitudes may be required in support of both daylight and night operations.
b. Antiaircraft gun batteries are difficult targets because they are small, usually widely scattered, and are easily moved. They may easily be discovered when firing, but such batteries ordinarily will not disclose their positions by firing until the defended objective actually is threatened. The plan of assault normally is based on the direction of approach of the supported bombardment unit. In order to cover every avenue of approach, the defending batteries are likely to be distributed over a large area in such a manner that only a portion of them can fire on bombers approaching at high altitude, prior to their arrival at the bomb release line.
c. The primary attack is made from the most favorable direction, and the minimum altitude support need be directed against only those batteries which constitute a threat to the success of the primary bombing mission.
d. The commander of the supported force supplies the supporting unit with information of the time of attack, the direction of approach, and the specific targets that will be attacked. The neutralization of antiaircraft gun defenses can best be accomplished by the direct assault against the batteries which can fire upon the supported bombardment unit.
e. During daylight the laying of smoke to obscure artillery fire control stations may have a satisfactory neutralizing effect. The most effective use of smoke requires accurate laying in accordance with a prior knowledge of fire control station locations. Direct assault of firing batteries, with destructive munitions, is preferable to the use of smoke.
f. An assault unit of three airplanes usually is sufficient to silence an antiaircraft battery. It is desirable that three such assault units be assigned for the neutralization of each two known or suspected batteries of artillery, the third unit to remain in the vicinity of the initial point to cover any unanticipated battery or to support the fires of the other units as required. Assault units operate from initial points located just beyond the effective range of the organic automatic weapon defenses of the batteries to be neutralized.
g. Arrival at initial points must be accurately coordinated with the approach of the leading unit of the supported force to within range of the antiaircraft artillery. Radio communication between assault units and with the minimum altitude combat commander facilitates the conduct of the mission. A pyrotechnic code may be used to supplement radio when necessary.
164. DAYLIGHT METHOD OF SUPPORT.-a. During daylight attacks, under conditions which permit accurate determination of the route or routes of approach of the assault units of the primary bombing attack, it is feasible to confine the minimum altitude operations to a zone within which anti-aircraft artillery batteries must be located in order to fire upon the supported bombardment force. The zone to be neutralized extends beyond the bomb release line, and on each side of the route or routes of approach of the high altitude bombers, to a distance corresponding to the maximum effective horizontal range of the defending antiaircraft artillery.
b. A plan for the minimum altitude support of a daylight bombing mission is shown graphically in figure 11. The figure shows the plan for a sector of approach for the several units of the primary (supported) bombing force. When the primary bombing force employs only one line of approach, the sector is reduced to a line or narrow lane, and the zone of effective antiaircraft gun locations is reduced accordingly.
FIGURE 11.-Diagram of minimum altitude support for a high altitude (main) attack against antiaircraft artillery defended objective.
165. NIGHT METHOD OF SUPPORT.--When supporting and supported forces approach their objective for night attack, searchlights of the opposing antiaircraft artillery will go into action. The supporting squadron leader directs his flights to the attack, one flight at a time. The flight moves to the attack with greatly extended interval, each individual airplane then attacking a single searchlight. If the searchlights attacked do not go out of action, or if others appear, the squadron leader dispatches a second flight. One supporting squadron of nine airplanes will normally be able to render ineffective all the searchlights that bear on the sector of approach of the supported force.
166. EFFECTIVENESS.-The effectiveness of minimum altitude operations in overcoming antiaircraft defenses arises from both neutralization and destruction. The presence of aircraft flying at minimum altitudes in the vicinity of anti-aircraft artillery defenses interposes a serious interference with the operation of the aircraft warning and fire control systems of the defending artillery. Such aircraft are vulnerable to the local machine gun defenses in the vicinity of the bombardment objective, and the plan of employment must provide for minimizing exposure to such fire.
SECTION IV: USE OF CHEMICALS
167. PURPOSE.-a. Chemicals normally are used to produce effects which cannot be obtained by other means. The principal purposes for which chemicals are employed are to neutralize areas of terrain in order to deny their use to the enemy; to produce harassing and casualty effects on personnel or animals; to screen areas; to conceal our own or interfere with enemy operations; and to secure incendiary effects.
b. Harassing agents, such as tear gas, are used to obtain the immediate though temporary effect necessary to interfere with and delay enemy operations. Casualty effects may be obtained by direct placement of either persistent or non-persistent agents upon personnel or by contamination, through the use, of persistent chemicals, of areas which it is desired be denied to the enemy.
c. Screening and obscuring effects are obtained by the use of smoke producing chemicals. Accurate placement from minimum altitudes is essential to the most effective use of smoke.
d. Incendiary agents are used to start fires when the desired results cannot be obtained by explosive force or case fragmentation. In many situations the requisite incendiary effect can be obtained by demolition bombs as result of momentary high temperature of burning explosive and of metal fragments. (See par. 36.)
168. PLACEMENT.-The placement of chemical agents, except chemical bombs, usually is accomplished from minimum altitudes. Placement is effected either by dropping chemical containers intact or by releasing the chemical agents directly into the air from containers which remain attached to the aircraft during release. Chemical containers attached to the aircraft are carried either externally or internally and may or may not be droppable during flight.
169. CHEMICAL BOMBS.-a. Chemical bombs are designed to be carried on racks suitable for other types of bombs and are released in the same manner as other bombs. In order to contaminate areas attacked by demolition bombs, persistent chemicals contained in chemical bombs may be dropped during the same mission. A high concentration within a limited area and hence greater persistence of the chemical can best be obtained by the use of chemical bombs. All types of chemical agents may be dispersed in chemical bombs.
b. All chemical bombs may be dropped from minimum altitudes because of the comparatively small booster charge. The dispersion upward is not sufficient to endanger the airplane.
170. CHEMICAL SPRAY.-The spraying of chemicals normally is accomplished at minimum altitudes. Smoke producing materials, tear gas, and toxic chemicals all can be effectively dispersed in this manner. It is an excellent means of dispersing tear gas, since the gas is effective in extremely low concentrations.
171. DISPERSION PROCEDURE.-Chemicals are normally dispersed by aircraft operating singly or by small assault units in flight formation. When chemical spray is released in formation, steps must be taken to avoid contamination of aircraft by the spray released from others in the same formation. It is best to release spray either from single aircraft or by an arrangement of assault units, which does not require any airplane to follow closely in the path of another. The number and arrangement of assault units for the dispersion of chemicals depend on the capacity or number of chemical containers, speed of aircraft, nature and extent of area to be covered, enemy antiaircraft defenses, and atmospheric factors involved.
172. CHEMICAL ATTACKS.-a. The indiscriminate dispersion of chemicals over a large or indeterminate area is both wasteful and ineffective. Each mission is directed against a definite area which the assault units can find and identify. The plan of attack is based on the size and shape of the area to be covered.
b. The path of the attacking aircraft should be across the wind so the chemical cloud will drift across the area instead of along the flight path of the dispensing aircraft. A cross drift is desirable regardless of the kind of chemical or method of application, whether by bomb or spray. Aircraft releasing chemical spray fly on the upwind side of the area it is to cover. The spraying of large areas requiring the release of chemicals along two or more flight paths always is initiated on the downwind side of the area, so that each succeeding airplane will release its spray along a flight path which is upwind from that of its predecessor, thereby avoiding contamination. The number of aircraft required to accomplish a mission in the desired concentration depends on the entire area to be covered as compared with that covered by a single airplane.
173. CONCENTRATION.-The concentration requisite to effective results depends upon the chemical used and the nature of the objective. Chemical bombs afford a high concentration but the area of effectiveness of each bomb is relatively small. The concentration obtained in chemical spraying depends on the speed of the dispensing aircraft; rate at which the chemical flows from the spray orifice; altitude at which released; and wind velocity.
174. LONGITUDINAL COVERAGE.-The longitudinal coverage of a single airplane depends upon its speed, amount of chemical carried, and rate of discharge. The distance which the aircraft fly during the discharge of the full capacity of tanks at the rate requisite to obtain the desired concentration represents its maximum longitudinal coverage by chemical spray. The use of multiple tanks enables single airplanes to conform to lesser longitudinal coverages without undue wastage of chemicals and permits a degree of control of concentrations. When bombs are released in train, the length of the train represents the longitudinal coverage per airplane.
175. LATERAL COVERAGE.-a. A single airplane can cover only a relatively narrow strip by the train release of bombs. The affected area becomes somewhat widened by the subsequent cloud drift resulting from a cross wind. The lateral coverage of a single airplane using chemical spray depends upon the velocity of the wind across the flight path and the altitude at which the spray is released. Accuracy of placement is difficult, except at very low altitudes, unless accurate information of the wind velocities at and above the surface is available. The cloud formed by chemical spray travels with the wind and retains its effectiveness in causing casualties and harassment for considerable distances. The rate of diffusion and cloud drift may vary considerably, but the figures contained in table VIII, based upon experimental determination, may be used as a general guide. The distances stated in the table are average results and are reliable within 10 percent for distances of more than 500 yards, in connection with the spraying of either lachrymation or vesicant chemicals on personnel or the laying of smoke screens.
TABLE VIII.-Lateral coverage by chemical spray
(Wind velocity 5 to 10 miles per hour)
b. Lateral coverage is illustrated in figure 12 for the conditions stated thereon.
c. When the width of the area to be covered exceeds the lateral coverage obtainable by one airplane under the conditions attending the performance of the mission, the number of flight paths is increased accordingly.
176. SMOKE SCREENS.-Smoke screens are used for purposes of concealment or interference, and their effectiveness depends upon the accuracy of placement and adequacy of the density of the smoke cloud produced. Concealment against the horizontal vision of an observer on or near the surface is assured only when the smoke screen is so laid as to extend downward to the surface. The requisite density for horizontal concealment is obtained by the laying of smoke along a single flight path. The screening of aircraft at high altitude against observation from antiaircraft fire control stations or other observers on the ground usually requires a smoke blanket of greater width than can be obtained by releasing smoke along a single flight path, and two or more lines of smoke are merged in order to form an effective blanket.
FiIGURE 12.-Fall of liquid drops (to 22-gallon tanks operated simultaneously.)
177. DRIFT of SMOKE CLOUDS.-a. The behavior and duration of smoke clouds depend on initial smoke density and on the character and velocity of air movements. The cloud will maintain its density for a considerable time in a steady wind of moderate velocity but may soon be dispersed by a strong or gusty wind.
b. A single line of smoke will provide a satisfactory screening effect while drifting from 3,000 to 4,000 yards from the original line, in steady winds of from 2 to 25 miles per hour velocity.
c. The wind carries the smoke upward and forward in such a manner as to spread it. The leading edge of the cloud usually travels approximately one and one-half times as fast as the wind velocity 6 feet above the ground, and the trailing edge, being retarded by contact with objects on the surface, moves at approximately eight-tenths of the wind velocity.
d. Computation of the probable drift and spread of a smoke cloud can be based on the figures stated above.
Example: To compute the approximate width of a sprayed cloud 6 minutes after it is laid across a surface wind of 10 miles per hour:
Leading edge:
6 min. x 
yds. per min. x 1.5=2,640 yds.
Trailing edge:
6 min. x 
yds. per min. x..8=1,408 yds.
The difference is the width of cloud, which equals 1,232 yards.
178. MERGING OF SMOKE CLOUDS.-Clouds laid by separate airplanes along parallel flight paths drift and spread so as to form a continuous smoke blanket. Data relative to intervals between flight paths and rates of merging, determined by experimental test, are as follows:
SECTION V: ATTACK OF NAVAL OBJECTIVES
179. GENERAL.-a. The attack of naval objectives is required in bombardment operations performed in lieu of or in support of naval forces.
b. Important naval objectives normally will be defended both by antiaircraft guns and by fighter aviation. The technique of minimizing losses from hostile antiaircraft fire is the same in the attack of naval objectives as in the attack of objects on land.
c. The requirements of successful attack against naval objectives are fourfold:
(1) Naval objective must be located.
(2) Location must be reported to assault units.
(3) Attacking aircraft must reach the target.
(4) Requisite number of hits must be obtained.
d. The differences in the technique of air attack of naval objectives and of objectives located on land arise principally from the need for search operations to locate the objective, and the maneuvering tactics which the objective may employ during the actual bombing.
180. SEARCH METHODS.-The search operations required for air attacks of naval objectives will be conducted in general accordance with the provisions of FM 1-20. Where possible, widespread search operations over long periods of time are to be avoided since they exert an uneconomical wear and tear on personnel and equipment. Usually consideration of economy of force will dictate the utilization of a portion of the force in search, another in shore reconnaissance or surveil-lance, and another, preferably the major portion, in reserve in some convenient locality prepared to strike en masse after the objective has been located. The proportions devoted to search, surveillance, and mass attack depend upon the character and strength of the naval objective, probable mission of the enemy and his most probable route, and amount of friendly bombardment force available.
181. COMMUNICATION.-Radio silence is normally maintained during bombardment attacks against naval objectives. It is broken only to make necessary contact reports which are kept as brief as practicable and rendered without delay. Other aircraft of the attacking force converge upon the airplane reporting contact and thereafter visual signals are utilized. It is desirable that the several elements of an attacking force maintain continual visual contact whenever practicable. The assembly of an attacking force solely by the utilization of radio homing devices depending on brief contact reports for guidance is extremely difficult and also dangerous, because hostile fighter aviation forces may use the same signals to effect interception.
182. ADVANCE TO OBJECTIVE.-Striking forces may proceed seaward against naval objectives in one of three ways:
a. The striking force may be held at some convenient location prepared to proceed to the objective after its location is reported by reconnaissance agencies.
b. The striking force may proceed as a unit in the general direction of the objective, departing its base area prior to the target being located, and depending on the reception of radio advices en route concerning the exact location of the hostile naval force.
c. The striking force may proceed seaward in search attack, planning to assemble and attack after location of the target.
183. SEARCH FOLLOWED BY ATTACK.-a. When widespread areas extending long distances seaward must be searched for naval objectives that require the effort of a squadron or more of aircraft for their destruction, it is preferable to operate by the first method outlined in paragraph 182, that is, search followed by mass attack. The necessity for carrying bombs reduces the operating radius of the searching aircraft. Also the best disposition of aircraft for searching an area does not permit the participating aircraft readily to be assembled for the performance of air attack. However, the time required by the search, the fleeting nature of the objectives, and the limitations imposed upon successful air attack by periods of unfavorable weather and/or darkness may in some situations demand attack without the delay incident to the first method of paragraph 182. It is, therefore, usually essential that naval objectives be attacked with minimum delay. Except under very favorable conditions, the attack of naval vessels is restricted to periods of daylight. The exceptions occur when excellent moonlight and visibility favor tracking and bombing missions without artificial illumination, or when the location of the target in a river, harbor, or other small water area makes feasible the use of flares.
b. The conduct of bombardment units in formation flight to the initial points for assault involves considerations similar to those governing the attack of land objectives.
184. DEPARTURE EN MASSE PRIOR TO TARGET DISCOVERY.-The second method of reaching the objective, listed in paragraph 182, can be employed to reduce the limitations imposed on air attack by the darkness period, especially when the direction of travel and general locality of the enemy are known or canalized by circumstances. If, however, the width of the zone in which the enemy may appear is great, darkness may intervene and render attack difficult.
185. SEARCH ATTACK.-a. This operation finds its most effective application in the attack of cargo vessels and other naval forces requiring for their destruction only a small bombardment unit effort. It is useful also in the execution of a minor search, such as the search of a position circle of a discovered target with which contact has been only recently lost. Although search attack of widespread areas should be avoided whenever practicable, occasions will arise where, due to the necessity for using bombardment airplanes for reconnaissance or to save time in delivering the attack, search attack will be required.
b. When the coverage required permits, and visibility is variable or not reliably known, search attack is preferably conducted by scouting units of a flight or larger on each scouting path.. This disposition of the force favors increasing the number of scout paths when areas of reduced visibility are encountered, and also provides some small measure of mutual protection.
c. An alternate method of search attack when the visibility and the size of the area to be searched permit is to cover the area with a portion of the force spaced on scout paths, following in a centrally located position with the remainder of the force as a unit.
186. ASSAULT OF NAVAL OBJECTIVES.-a. The naval objectives against which bombardment aviation may operate include the armed vessels of a hostile fleet, auxiliary vessels, supply ships, troop transports, merchant vessels carrying war supplies, and vessels serving as reporting stations of an aircraft warning service. The appropriate sizes of bombs for use against various categories of naval objectives are shown in table IV (see appendix)
b. The type and size of bombs carried on missions against naval objectives are determined by the character of the objective of first priority. The number of bombs carried in each airplane is dependent upon the bomb rack capacity, amount of fuel required for the accomplishment of the mission, and over-all permissible load of the airplane. The size of the force required is determined by the number of bombs required to insure the requisite number of hits under the controlling probability factors.
c. The objectives normally are attacked in the assigned order of their priority. The entire area of probable target location is searched for objectives of first priority before attacking those of lower priority. A prescribed order of priority is justified by the comparative importance of the several types of vessels and by the variation in suitability of the various sizes of bombs against the several types of vessels. Bombs some-what smaller than those most appropriate to the attack of any particular class of naval vessel, though not as effective as the correct size, will cause serious damage and may be used when necessary.
d. Armed vessels normally operate in formations suited to the conduct of naval warfare. They usually are well protected by antiaircraft guns of both small and large calibers. Large naval forces are likely to have strong pursuit forces for use in antiaircraft defense. Unarmed vessels, constituting important objectives for air attack, are likely to be provided with an armed convoy possessing strong antiaircraft defenses. The technique of penetrating antiaircraft defenses of naval objectives is similar to that for the penetration of the anti-aircraft defenses of land targets, with such modifications as are made desirable by differences between naval and land defensive equipment.
e. The attack of naval objectives defended by antiaircraft artillery with demolition bombs is accomplished by precision bombing methods normally from high altitude. Such high altitude operations may be supported by minimum altitude missions to lay smoke or otherwise neutralize antiaircraft guns. Dive bombing attacks are effective against naval objectives.
f. Minimum altitude attacks with fragmentation bomb, machine guns, and toxic chemicals are effective against expeditionary forces on transports during debarkation and landing operations.
g. The axis of attack should be selected after balancing the advantages accruing from the use of the various directions of approach. Advantages must be considered both from the offensive and the defensive point of view. The axis selected will be a tactical decision in each case.
(1) Considerable masking of antiaircraft artillery gunfire can be secured by attacking along the fore and aft axis of the defensive surface vessels.
(2) High speed through the antiaircraft fire zones materially reduces the number of shells that can be fired at the attacking aircraft. Therefore, a defensive advantage accrues from attacking from that direction which, considering wind velocity and the speed of the target, provides the greatest relative speed between the objective and the attacking aircraft. Offensively, the accuracy of bombing is somewhat reduced by the higher relative speed.
(3) Normally, a direction of attack within 30° of the direct sun-battery or moon-battery line causes considerable loss to the antiaircraft artillery defenders in their ability to pick up the approaching planes, and thus delays the initiation of the defensive artillery fires.
(4) Penetration of the gun defenses in a weak sector is very desirable. In this case the effective range of the antiaircraft guns will vary with the equipment used by the enemy.
(5) From the offensive point of view, an attack from the stern down the direction of the target travel makes feasible a method of minimizing the effects of the defensive maneuvering of the vessel.
187. TARGET MANEUVER.-Naval objectives are capable of sufficient maneuver adversely to affect high altitude bombing accuracy. Their maneuverability includes change of speed and change of direction, the latter being the most effective in avoiding aerial bombs. The degree to which vessels in battle formation can maneuver, particularly during an active naval engagement, is materially restricted because of the necessity of maintaining proper position in the battle formation and because of the adverse effect of maneuver on gunnery accuracy. Aircraft carriers, even when not restricted by the necessity of conforming to the movements of other vessels, cannot engage in abrupt maneuvers during the launching or landing of their aircraft. Computations based on the observation of the approaching bombers will facilitate the initiation of a change of direction practically coincident with the release of bombs. There is an appreciable interval after the movement of the rudder before the naval vessel actually changes its direction of motion. This interval varies for different vessels. Under favorable circumstances an experienced bombardier can observe the change in the wake, resulting from rudder movement, and thereby anticipate by several seconds an impending change of direction. A change of direction results in sufficient departure from the original course to avoid aerial bombs only when the vessel has a fairly high forward speed. Reversing engines or materially reducing speed is not favored by naval authorities, because by so doing the vessel sacrifices its ability subsequently to change its position by maneuver.
188. MANEUVER AREA.-a. After an accurately aimed bomb has been correctly released from high altitude, a maneuvering naval objective may change course and avoid the bomb impact, even though vessels which are profitable bombardment targets are of such size as to have a relatively low rate of change in speed or direction or both. However, a satisfactory probability of hitting a maneuvering target can be attained by the application of a bombing pattern of adequate density to the entire area in which the target vessel can possibly be when the bombs strike. This method of attack is wasteful of bombs, and it is necessary, therefore, that the size of the maneuver area be ascertained fairly accurately in order that bombs may not be dropped where they cannot possibly be effective.
b. The actual size of the maneuver area available to the vessel during the fall of the bomb varies with the bombing altitude, the bomb ballistic characteristics, and. the vessel speed, tactical diameter, and design conveniences for reversing power. This area may also be reduced if the vessel fails to initiate its maneuver at the proper instant. Obviously some variations in the plans of attack will be advisable against varying equipment and enemy doctrines of operation. An example follows of one method of attack which presumes, for the surface vessel, perfection in the timing of its maneuver and full use of changes in speed and direction. In this example the objective is a vessel that by the application of standard rudder can turn 180° in 1,000 yards, which is therefore by definition the tactical diameter. The vessel speed is assumed to be 30 knots. Reasonable average data are used elsewhere throughout this example.
c. Figure 13 shows a situation in which at zero time standard rudder was applied to the vessel, but in this case turning initiated at zero plus 18 seconds. At precisely this time the bomb is assumed to be released at an altitude of 18,000 feet. By use of different rudder settings at full speed, the center of gravity of the vessel may reach in the times indicated any point on the various loci shown.
d. The position of the vessel may further be affected by changes of speed. Of particular importance to the bombardier is the area in which the vessel may be located at the instant of impact of the bomb. This area is shown in figure 14 by shading superimposed on a diagram similar to that of figure 13. Variations in the data, such as changes in assault altitude or vessel characteristics, will modify the maneuver area.
189. ASSAULT METHODS.-a. Considering the maneuver area shown in figure 14 as the target, the method selected for assault should be adaptable to pattern bombing covering this area. When assault units consist of waves of nine bombers in squadron stagger formation, the area can be covered in the manner described below.
FIGURE 13.-Areas of possible locations of vessels (maneuvering targets) having 30 knots' speed at zero time and tactical turning radius of 500 yards.
b. On nearing the vicinity of the bomb release line, the right and left flights diverge to the right and left, respectively. The three flights then converge in their bombing approach to the bomb release line as shown in figure 15. For an altitude of 18,000 feet, and for the example in figure 14, the angle of convergence of flight axes of attack is approximately 30°.
The angle of convergence increases with the bombing altitude. In figure 15 are shown three flight patterns of twelve bombs each, released in train at 1/2 second intervals at 200 miles per hour. Superimposed on the maneuver area is the silhouette of a vessel with a danger space surrounding it. The leading flight has bombed as though no maneuver was anticipated, the right and left flights covering the flank portions of the maneuver area with their patterns.
d. Since the bombs of the flight away from the direction of vessel maneuver are wasted in the method discussed in b above, an alternate method of assault may be used, wherein the flights approach the bomb release points at a specified short interval, to permit succeeding flights to sense the direction of vessel maneuver prior to release of their bombs.
FIGURE 14.-Area in which vessel (maneuvering target) can be at time of impact of bomb.
c. Bombs should be released in train at such interval that the space between bombs is small enough to prohibit bracketing the target with two adjacent bombs irrespective of its location. The train length should be such as to provide full coverage of the maneuver area. Obviously a compromise between these two desirable details is necessary when the bomb-load that can be carried is insufficient to permit proper density throughout the maneuver area.
FIGURE 15.-Diagram for assault of vessel (maneuvering target).
190. SIZE of FORCE-a. The size of the force to be used against naval objectives depends on the nature and number of target vessels, their defenses and ability to maneuver, the desired degree of certainty of success (usually 90 percent) , the bomb capacity of the aircraft on the mission, and the accuracy of the bombing crews under the conditions of the assault. Maximum economy of bombs and minimum strength of force are achieved against still targets when each bomb can be separately sighted and dropped from an individual assault airplane. Airplanes may attack naval objectives singly when they are undefended and other conditions are favorable to that method of assault. However, naval targets which are free to maneuver should normally be attacked by aircraft in formation in order to secure the requisite bomb pattern.
b. Objectives defended by antiaircraft guns should, when practicable, be attacked by a force of such size that the number of individual airplanes exceeds the estimated number of enemy antiaircraft fire control directors able to operate against the attacking aircraft. Usually against strong naval dispositions this will not be the controlling factor in determining the size of the attacking force, since the desired assurance of success will require many more aircraft than the number of hostile naval antiaircraft directors.
c. As in the case of the attack of land targets, attacks of naval objectives should be made as nearly simultaneously as possible, with a force sufficient in size to assure that, with deductions for losses en route, the proper number of bombers will reach the bomb release line to effect the desired destruction.
191. BOMBING ALTITUDE.-Naval objectives free to maneuver are bombed from the lowest altitude consistent with bombing accuracy and proper security measures. Obviously, the lower the bombing altitude, the smaller the opportunity of the vessel to avoid the bombs by maneuver. Strong antiaircraft gun defenses may require a high bombing altitude to reduce the effectiveness of the antiaircraft guns. Normally, due to their importance and fleeting character, strong naval forces require a 90 percent chance of success on each mission. This high percentage may necessitate so large a force of bombers, if employed at high altitude, that some compromise with security will be justified by the importance of destruction of the objective.
192. MINIMUM ALTITUDE ATTACKS.-a. Bombing attacks against naval objectives may be accomplished at minimum altitudes by the use of torpedoes under circumstances which do not permit the employment of normal bombing methods. Examples of such conditions occur when, due to the presence of low clouds, attacks must be made at altitudes so low as to make relatively dangerous or ineffective the use of aerial bombs. In very low altitude attacks, the explosion of the bomb dropped with instantaneous fuze is likely to damage the attacking aircraft. On the other hand, the bomb fuzed with sufficient delay to assure the safety of the airplane may explode at too great a depth to injure the surface vessel.
b. Minimum altitude attacks in support of the high altitude bombing attacks are useful in neutralizing the fire of antiaircraft guns. Such attacks are more difficult over water because of the absence of the cover usually provided in land operations by irregularities in the terrain and the presence of wooded areas. The smoke screens laid by surface vessels during naval engagements provide excellent horizontal cover to aircraft engaged in minimum altitude attacks. The minimum altitude technique employed against objectives on land is effective against naval objectives. (See pars. 94, 108, 110, 116, and 186f.)
SECTION VI: COUNTER AIR FORCE OPERATIONS
193. GENERAL.-a. In counter air force operations, bombardment aviation is employed in air attack to deny the enemy all or partial use of his aviation forces. Such operations are offensive in nature, as distinguished from antiaircraft defense action against enemy aircraft in flight. Bombardment objectives for counter air force action should be selected after consideration of the following factors:
(1) Relative importance of the targets, from the point of view of the immediate, lasting, and cumulative effect of their destruction or neutralization.
(2) Capacity of the friendly air force to effect destruction or neutralization.
(3) Probable losses involved in the counter air force operations.
b. If reasonably within the capacity of the force and not prohibitive in losses of friendly aircraft, the priority of counter air force objectives is as follows:
(1) Aircraft.
(2) Operating personnel.
(3) Air base facilities, including landing areas, maintenance and overhaul shops, local supplies, and routes of communication.
(4) When the enemy aircraft are carrier based, the destruction of the carrier or carriers is the primary objective of counter air force action.
(5) Advanced refueling airdromes essential to the enemy.
(6) Concentrated supplies, either stored or in transit.
(7) Lines of communication essential to supply and replacement.
c. Because of the difficulty of counter air force action, occasions may arise where the force available may be too small to achieve complete success, no matter how employed. In some instances, losses may be severe. However, where counter air force action is of paramount importance, that method of operation which promises to inflict the greatest handicaps on the enemy should be adopted, though only partially successful. In balancing our losses against those inflicted upon the enemy, it must be borne in mind that the loss of use of airplanes is actually the loss of potential destructive power. From this point of view, it may be profitable to accept heavy losses of our own aircraft, if we deny the enemy air action against our vital ground installations within his radius of action.
194. ATTACK OF AIRCRAFT.-a. Aircraft are particularly vulnerable to air attack when at rest in the open on the surface. Their destruction is by no means simple, however, because of their fleeting character and because of the difficulty of locating them. This latter is especially true of water-based seaplanes that may utilize sheltered waters and the cover of protective foilage along shore lines. Such craft constitute an elusive objective that can maneuver on the water or even take-off if sufficient warning of an attack is given them. Landplanes do not, in general, have the wide choice of landing points, but, when revetted, form unprofitable point targets. The general revetment area containing hostile aircraft should be regarded as an area target, and bombs distributed therein. During refueling and loading operations, an attack directed against aircraft finds them in a most vulnerable location, and usually results in incidental losses to personnel and materiel essential to the enemy's sustained operations.
b. Within a given weight of loading, small fragmentation bombs are the most effective against aircraft in the open. Demolition bombs with instantaneous fuzes may be used. For a given weight of bombs, the small demolition bombs are more effective than the larger sizes. Chemicals may be used to neutralize aircraft on the ground, but are relatively ineffective against seaplanes when the enemy is prepared for de-contamination. Against aircraft in revetments, small demolition bombs or chemical bombs are effective. The chemical bomb is effective in contaminating and damaging the airplane if a hit inside the revetment is secured. At the same time contamination of the revetment area is accomplished by those bombs that miss. The small demolition bomb requires a hit within a revetment to be effective.
c. Seaplane anchorages will not usually be adequately defended by active elements of antiaircraft defense, due to the difficulty of maintaining