Aircraft technical Basics: Introduction to Airplanes - Navy Training Courses Edition of 1944: Chapter 14 Armament

CHAPTER 14 ARMAMENT

MACHINE GUNS

In the early days of military aviation, airplanes were looked upon primarily as a means of obtaining information about the enemy. Then, according to legend, a World War I aviator had a brainstorm one day and FIRED HIS PISTOL at an enemy flier. After that everybody realized, all of a sudden, that here was a brand new weapon - THE ARMED AIRPLANE - and an aircraft armament race began. It's still going on full tilt.

During World War I the .30 CALIBER MACHINE GUN became the accepted standard for airplane armament. It did an excellent job, offensively and defensively, when you consider the task it had to perform in those days. It was inevitable, though, that the experts would work out ways to protect airplanes against .30 caliber gunfire. Better engines, for instance, made it possible to equip airplanes with ARMOR that would stop .30 caliber bullets and safeguard pilots without sacrificing too much speed in carrying the added weight of the armor.

Throughout all military history heavier armor has always been answered by heavier guns. So it has been with the airplane. Enemy craft, equipped with armor which would turn away .30 caliber ammunition, now could escape. A more effective gun became necessary, and a .50 CALIBER MACHINE GUN, already proved and in production for the ground forces, was soon adapted for aircraft use.

Figure 45.-Fixed guns in an airplane wing.

At first the ".50" was used only for fixed gun installations in FIGHTER airplanes, where it was found to be very effective. Within a short time, the .50 caliber gun was also put to work in BOMBER type airplanes, flexible mounts being provided for them. In some few cases, small bombers were also fitted with FIXED guns. On a bomber, however, you can't defend yourself completely with fixed guns, because they must be aimed at the target by maneuvering the airplane. Bombers just won't maneuver that easily. On the other hand, unless very firmly mounted, FREE guns installed in bombers are inaccurate at best, because free gunners are upon unsure footing when such airplanes are maneuvering or are flying in bumpy air.

The best answer to the problem of bomber armament was found in the POWER-OPERATED TURRET, a piece of equipment, which holds the guns steady during all maneuvers and in rough air. Moreover, the turret enables the gunners to bring their guns to bear at angles not previously possible in an airplane with hand-operated guns.

FIXED GUNS are rigidly mounted so as to fire in a direction practically parallel with the line of flight. Some fixed guns are synchronized to fire between the blades of the propeller. Others are mounted within the wing, as you see in figure 45, so that their line of fire clears the propeller blades. Such guns are operated by the pilot, who directs their fire by maneuvering the airplane. FLEXIBLE MACHINE GUNS are mounted in a way that permits them to be aimed at a target regardless of the direction in which the airplane is flying. Turret mountings combine the firmness of the fixed guns with the freedom of movement of the flexible guns. Actual battle experience has proved that turret guns are very effective, particularly against enemy aircraft which are not so equipped.

You will find flexible machine guns, other than turret-mounted guns, on certain types of air-planes, however. They are still very useful under certain conditions. One of these types is the TUNNEL GUN, which fires downward through a tunnel or opening in the fuselage. Although its freedom of movement is restricted, it provides effective fire in areas that are beyond the firing zones of the other guns on the airplane. The BRACKET-MOUNTED GUN is another type. It is fired through an opening in the side of the fuselage. It serves the same purpose as the tunnel gun. A bracket gun appears in figure 46.

It is necessary to use ADAPTERS in installing either fixed or flexible guns in an airplane. These adapters are furnished as accessories. FIXED GUN-MOUNT ADAPTERS are quite simple, consisting of a REAR MOUNTING POST ASSEMBLY and a TRUNNION-BOLT ASSEMBLY. The mounting post incorporates a quick-detachable feature that permits the gear to be removed and reinstalled in a minimum amount of time. FLEXIBLE GUN-MOUNT ADAPTERS are somewhat more complicated, since they must permit the gunner to train, elevate, and depress the gun as required. Practically all machine gun installations on FIGHTERS today are of the .50 caliber type, in fixed mounts. SCOUT BOMBERS usually carry BOTH fixed and flexible guns, as do SCOUT-OBSERVATION air-planes and TORPEDO BOMBERS. Turrets are also installed on many of the latest torpedo-bomber models and patrol bombers.

Packing more sockeroo than anything previously carried in the way of armament is the 20-MM. AUTOMATIC GUN. This gun was developed as the next logical step in increasing the airplane's firepower. More and more of the new airplanes have them installed in the form of fixed wing mounts. Because of the nature of its firing mechanism, this gun cannot be adapted for use as a synchronized gun - that is, to fire between the propeller blades.

TURRETS

Turrets, which you see on many of the larger aircraft, are the small round, glassed-in "green-houses" in which the gunner sits. You can see a turret in figure 46. In general, there are four main locations for turrets on various airplanes.

The UPPER TURRET, is located in the upper part of the fuselage to guard against attack from above. The LOWER TURRET is in the lower part of the fuselage to ward off punches "below the belt."

The REAR or TAIL TURRET protects the airplane against stern attacks. The NOSE or BOW TURRET guards the airplane's forward area.

Although turrets add to an airplane's weight, they make it possible to reduce the size of the crew carried. The result of this is that there's no need to reduce the useful load, or to weaken an airplane's fire power because of the turrets. With hand-operated guns, one operator is required

Figure 46.-Flexible guns: turret mounted (left); bracket mounted (right).

for each weapon, while in turrets one gunner can control the fire of several guns. Moreover, firing from a turret is more accurate, since the gunner doesn't have the problem of trying to keep a hand-held gun steady in the slipstream during flight.

The power-driven mechanism of a turret turns the turret horizontally and also elevates the guns vertically. In some turrets the guns all fire together. In other types they may be fired separately OR together, as the gunner desires. The amount of movement a turret can make - and therefore the field of fire of its guns depends upon the type of airplane in which the turret is mounted, and its position in the airplane. Almost all turrets nowadays are fixed up with INTERRUPTER devices which make it IMPOSSIBLE for the gunner to fire into HIS OWN airplane.

SIGHTS

Any gunner will tell you that one way to keep from growing old is to handle an airplane machine gun as if it were a hose pipe, and hope for a hit. The fire from such a gun isn't worth a Japanese nickel unless it's accurately aimed, and the hose-pipe method will let the enemy gunner get the drop on YOU EVERY time.

Good gunners must know how to use their GUNSIGHTS. Mechanically, your aerial gunsights are the best in the world, but they will only be 100 per cent effective if you know how to use them properly.

The function of a gunsight is to aid the gunner in aiming his weapon so that the bullets will hit the target. Aerial gunsights are more complicated than those found on rifles and similar weapons. A projectile or bullet fired from a gun in an air-plane does not travel in a straight line to the target. Instead, the forces encountered by the bullet in the air make it take a curved path  known as the TRAJECTORY. So special gunsights are needed to aid the gunner in determining where to point his guns so he'll hit the target.

The ordinary aerial gunsight consists of a RING PEEP and a BEAD. This arrangement is a lot like the sights of a rifle, except for the ring encircling the peep, which helps the gunner estimate the speed, range, and direction of the target. Errors are quite likely to creep in when you're using such MECHANICAL sights, however, and OPTICAL sights have been devised to eliminate these errors. Sometimes both types of sights are mounted on an aerial gun, so that the more rugged mechanical sight will be ready for use in case the fragile optical sight goes out of commission.

There are a number of different kinds of optical sights used on the Navy's aerial guns, such as OPTICAL ILLUMINATED SIGHTS, AUTOMATIC COMPUTING SIGHTS (which include an optical system, a range finder, and an automatic computing mechanism), and TELESCOPIC SIGHTS. Each has some advantages for particular purposes, and all offer better results than mechanical sights. All gunsights on airplanes are classified as either FIXED, or FLEXIBLE, according to the type of gun with which they're mounted.

HARMONIZATION AND BORESIGHTING

As explained above, the aerial gunsight aids the gunner in correcting for the forces which affect the bullet. The most accurate gunsight, however, will fail in its purpose if it and the gun (or guns) are not properly adjusted in relationship to each other.

Such adjustments are called HARMONIZATION.

When the guns and sights are harmonized -and the sights are used properly - the bullets will strike in the proper position on the target, as indicated by the sight.

In aerial gunnery there are certain factors which limit the effective lethal range of the guns. This doesn't mean that the bullets will do no damage beyond that range, but that the number of bullets concentrated in a given area on the target will be too few to justify firing. For this reason, guns and sights are harmonized for a specific range. To do this it is necessary to set up a PATTERN at the desired distance, and harmonize the guns and sights on this pattern so that the bullets will intersect the line of sight at the specified range.

As this range may be as much as 1,200 feet, circumstances may not permit use of the full distance for boresighting. In such case the same results can be obtained by sighting the guns and sight at a specially prepared pattern placed, say at a distance of 300 feet.

The successful harmonization of guns and sight on the pattern depends largely upon the ability of t he man who is assigned to BORESIGHT the guns. Boresighting is essentially the job of sighting through the bore (or barrel) of a gun and making the required adjustments to achieve harmonization.

AMMUNITION

The ammunition for aerial machine guns is issued in the form of fixed rounds, ready for firing, the complete round being loaded into the gun as a unit.

The principal types used are

BALL - for use against personnel and light material targets.

TRACER - for observation of fire.

ARMOR-PIERCING - for use against armored objects, airplanes, vehicles, etc.

INCENDIARY - for igniting inflammable materials.

All types and models of .30- and .50-caliber am-munition have bullets with gilding metal (copper colored) jackets. The various types are identified by the following colors on the bullet tips

BALL -plain, no marking.

TRACER - a painted red tip.

ARMOR-PIERCING - a painted black tip.

INCENDIARY - a painted light blue tip.

DUMMY ammunition, which is used for testing the action of guns after repair, looks much like service ammunition, except that the case is perforated with three circular holes. In some cases, dummy cartridges are also plated a silver color to permit easier identification. You have to take reasonable care to prevent mixing service and dummy ammunition when belting ammunition for combat use. Dummies won't kill Japs !

Figure 47.-Ammunition for aerial guns shown smaller than actual size.

Ammunition for aerial machine guns comes packed in metal-lined wooden cases. On the labels of all cartons, on all packing containers, and on cards sealed inside the metal lining of each ammunition box, the contents are identified as to QUANTITY, TYPE, CALIBER, MODEL, and LOT NUMBER. Ammunition boxes also have special identifying markings in the form of colored bands. As these color bands do NOT agree with the markings of the ammunition itself, care must be exercised, in breaking out ammunition, until the meanings of the various color bands are thoroughly understood. Figure 47 shows the three principal types of aerial machine gun ammunition.

BOMBING

The BOMB is the second of the two major offensive weapons of Naval aircraft. Bombing is accomplished by HORIZONTAL BOMBING, DIVE BOMBING, SKIP BOMBING, and TORPEDO BOMBING. Each method requires special techniques, skills and equipment, and has its own special advantages and disadvantages.

HORIZONTAL BOMBING is done from HIGH, or moderately high, altitudes with the assistance of an elaborate BOMBSIGHT which makes corrections in the bomber's aim. Some of the factors which have to be taken into account are speed of the airplane, altitude, wind speed and direction, and the exact position of the airplane in space with regard to the target.

One of the advantages of horizontal bombing is that LARGE-CALIBER BOMBS can be dropped most effectively from HIGH altitudes. The speed of such bombs at the moment they hit the target is greater than in other types of bombing, so they have greater penetration. Since airplanes engaged in horizontal bombing fly at high levels, the effectiveness of antiaircraft fire is reduced to a minimum.

There are some disadvantages, however. A straight approach to the target is necessary just before bombs are released. During this period, the bombing airplane is more vulnerable to defending fighters and antiaircraft fire. Clouds are another problem, as they may interfere with the bomber's view of the target. In addition, the time required for a bomb to fall from high altitudes permits maneuverable targets to avoid bombs after they have been released.

DIVE BOMBING has been practiced by the Navy's air forces for many years. This method involves AIMING THE AIRPLANE at the target while in a STEEP DIVE, and releasing the bombs at a comparatively low altitude. Successful dive bombing depends largely upon the skill of the pilot, as you can well imagine. In favor of dive bombing are the surprise element in attack, increased accuracy because of the low release point, less chance for the target to maneuver during the drop of the bomb, and the speed of the bombing air-plane which makes it a difficult target for anti-aircraft.

On the other hand, bombs dropped at low altitudes by dive bombers may not obtain as much penetrating speed as desired. And there is sometimes danger of the explosive blast reacting on the bombing airplane and other aircraft following it in a dive.

The procedure known as SKIP BOMBING (or "masthead" bombing) has been developed during the present war. It requires the use of a simple BOMBSIGHT, and finds the attacking airplane pilot attempting to pierce the SIDE of the enemy vessel with his bomb - either by DIRECT HIT or by a RICOCHET from the surface of the water. Skip bombing has as its strong points increased accuracy, the probability that the bomb will burst inside the enemy vessel's hull, maximum speed of the attacking airplane can be used, and the fact that small, fast airplanes can be employed for this type of bombing.

The attacker is, however, more vulnerable to antiaircraft fire, and must usually be accompanied by other airplanes to help knock out enemy batteries. Accurate FUSE TIMING on the bomb is also essential. And, in ricochet attacks, there is the possibility that the bomb may leap completely over the target.

The AERIAL TORPEDO is a very effective weapon if the torpedo plane can avoid antiaircraft fire and be defended against attack by enemy aircraft. The torpedo itself is a PRECISION INSTRUMENT, and its damaging effect is great. The pilot of a torpedo plane must drop his torpedo in such a manner that a COLLISION COURSE with the target results. An aircraft torpedo runs at a speed of 35 to 40 knots, and, if properly adjusted, will stay on course, as it is not affected by surface wind or sea conditions.

Among the reasons for the effectiveness of aircraft torpedoes are that the airplane is in fully-controlled flight when the torpedo is dropped, and the big explosive charge of a torpedo does its damage below the target vessel's water line.

Torpedo planes are nevertheless highly exposed to enemy antiaircraft and fighters unless heavily protected by escorting airplanes. They must get within 1,000 yards of the target before releasing their missiles, and keep a straight course at low altitude.