Aircraft technical Basics: TM 1-409, Aircraft Armament and Pyrotechnics, 1941: XI. - Demolition Bombs And Fuzes

Section XI - DEMOLITION BOMBS AND FUZES

73. General. a. Purpose and scope.-Demolition bombs are designed for the destruction or demolition of materiel targets, the destructive effect being produced chiefly by the violence of the detonation, although fragments may cause additional damage, particularly when the detonation occurs above ground. All demolition bombs are arranged for double suspension in horizontal bomb racks, the center line distance of the two suspension lugs being 14 inches, except that for the 2,000-pound bombs, the center line distance is 30 inches. In order that a maximum weight of explosive filler may be used, the steel body is made as light as is consistent with the structural strength required to withstand impact stresses. The explosive filler is approximately 50 percent of the total weight of the bomb. Demolition bombs are painted yellow with markings in black.

b. Assemblies for special purposes.-All demolition bombs may be divided into two groups: the streamlined demolition bombs of the Mk.-series; and the cylindrical demolition bombs of the M-series.

Standard assemblies of the M-series of bombs use the fuze, bomb, M103 (nose) (fig. 12) and fuze, bomb, M106 (tail) (fig. 13). For use of the M-series of bombs in special missions (highly resistant targets), the fuze, bomb, M100, M101, or M102 (tail) (see TM 9-980), dependent upon the size of bomb, is sometimes authorized. In such cases the fuze, bomb, M103 (nose), is omitted. Standard assemblies of the streamlined bombs use the fuze, bomb, M103 (nose) (fig. 14), and the fuze, bomb, M106 (tail) (fig. 12). When the 45-second delay action of the fuze, bomb, M106, is required in any of the Mk.-series or the cylindrical M-series of demolition bombs, the nose fuzes (fuze, bomb, M103, or fuze, bomb, M105, as the case may be) must be made inoperative. This may be done by omitting the nose fuze, leaving the nose closing plug in place, and cutting off the unused portion of the arming wire; by removing the arming vane which is readily detachable; or by cutting the arming wire and so twisting the ends that the arming vane cannot turn. The first method is preferable; either of the other two methods may be used during flight, or on the ground when the situation so demands.

c. Functioning.-Functioning of bombs is primarily dependent upon the action of the fuze or fuzes fitted thereto. The action and functioning of each fuze is described in the paragraph devoted to that fuze. Fuzes designed for instantaneous, short delay (0.1-sec.), and long delay (45-sec.) actions are provided for demolition bombs. Instantaneous action is used for surface effect, that is, against targets which may be destroyed by the violence of the explosion. Short delay action is used to produce a mining effect or where it is desired that the bomb explode after it has penetrated the target. Long delay action, 45 seconds or more, is used for special purposes. With instantaneous action, the blast effect varies approximately inversely as the square of the distance and directly as the weight of the charge. With delay action, approximately 0.5 cubic yard of earth is displaced per pound of explosive.

74. Bomb, demolition, 100-pound, M30.-a. General-The principal data and marking of this bomb are similar to the system used on the complete round assembly shown in figure 10. It weighs approximately 107 pounds and is intended for destructive effect against such targets as railway equipment and trackage, small buildings, ammunition dumps, airplanes on the ground, hangars, etc. For the standard complete round assembly, the following components are required :

(1) Bomb, demolition, 100-pound, M30, unfuzed.

(2) Fuze, bomb, M103 (nose).

(3) Fuze, bomb, M106 (tail), or, for special missions, fuze, bomb, M100 (tail).

(4) Wire, arming, assembly.

b. Description-This bomb is a cylindrical type bomb having a box type fin. It contains approximately 57 pounds of high explosive and is adapted for both a nose and a tail fuze. To keep the fuze cavities free of foreign matter, closing plugs are fitted to the adapter openings.

c. Assembly and disassembly (fuzing and unfuzing).-The prior examination of components prescribed in a previous paragraph is for the purpose of insuring that all components at the bomb fuzing point are serviceable. For assemblies for special purposes, see TM 9-980. The standard complete round is assembled as follows :

(1) Tail fuze.-After removing the tail closing plug, assemble tail fuze as prescribed. Tighten fin lock nut if necessary.

(2) Nose fuze.-After removing the nose closing plug, assemble nose fuze as prescribed. The bomb is now an assembled complete round ready for installation in the bomb rack.

Note.--After the bomb has been installed in the bomb rack, the cotter pins are to be removed from the fuzes in accordance with instructions on the tags attached thereto. Should it be necessary to disassemble the complete round into its components, the above steps will be carried out in the reverse order and the components restored to their original condition and packings.

d. Fuzing procedure.-The procedure in the fuzing and handling of all M-series bombs is the same. All bombs of this series use the bomb fuzes, M103 (nose), and M106 (tail), except for special missions.

e. Designations and weights-Listed below are the designations and weights of the M-series of cylindrical demolition bombs :

(1) M30-100 pounds.

(2) M31-300 pounds.

(3) M32-600 pounds.

(4) M33-1,100 pounds.

(5) M34-2,000 pounds.

(6) M43-500 pounds.

(7) M44-1,000 pounds.

75. Fuze, bomb, M103 (nose) .-a. General.-This fuze is a selective, instantaneous, and short delay arming vane type of fuze in which the primer, detonator, and booster are made an integral part thereof. Additional features incorporated in this fuze include a mechanical delay arming mechanism and detonator safety. The arming vane is shipped unassembled to the fuze. The fuze may be set for either instantaneous or short delay action by means of a setting pin which projects from the side of the body. When shipped, the pin is in the deep slot or delay position. To set for instantaneous action, lift the pin, rotate one quarter turn, and drop it into the shallow slot.

b. Description (fig. 12).-The selective action of this fuze is obtained by the use of two firing systems, one for instantaneous action, the other for delay, both being contained in the upper part of the body. The detonator is mounted in a slider located below the firing pins and is normally held out of firing position by the arming stem. In this out-of-firing position the detonator communicates with a cavity into which the force of the explosion of the detonator could expand should the detonator function prematurely, thereby providing a detonator-safe fuze. In the arming of the fuze, the arming stem also serves as a stop to limit the movement of the slider to the position appropriate for the required action-instantaneous or short delay-dependent upon the setting of the setting pin. The booster, a tetryl pellet, is contained in the bottom of the fuze. Delay arming is accomplished by interposing a reduction gear train between the arming vane and the arming screw, thereby reducing the movement of the arming screw to one turn for approximately 65 revolutions of the arming vane. Arming disks, between the striker and the body of the fuze, prevent movement of the firing pins prior to arming. The detachable arming vane is held in position by a spring vane, holder ring. Eyelets in the vane strap, which aline with corresponding eyelets attached to the vane cup are provided for the arming wire. The fuze may be set at will, instantaneous or delay, at any time.

c. Assembly and disassembly (fuzing and unfuzing).-No attempt will be made to disassemble the fuze. The only authorized assembling operations are those required to assemble the fuze to the bomb as described in detail below.

(1) Remove fuze from sealed metal container.

(2) Cut and remove seal wire, complying with instructions on seal tag.

(3) Screw nose fuze, less vane assembly, into the nose of the bomb until it seats-handtight, using no tools.

(4) Thread the shorter end of the arming wire through the front suspension lug of the bomb and through the nearer pair of eyelets. Should the nearer pair of eyelets be occupied by the cotter pin and tag, place a second cotter pin through the pair of eyelets diametrically opposite before removing the original cotter pin. This cotter pin is not to be removed finally until after the bomb is installed in the airplane (see note on tag).

(5) Adjust arming wire to protrude from 2 to 3 inches.

(6) Slip one safety clip over end of arming wire until it just touches face of the vane strap.

(7) Slip vane assembly over vane holder so that the heads of the two vane pins enter mating holes in the flange of the vane holder and the vane holder spring snaps into the groove on the vane holder. The fuze is now completely assembled to the bomb, except that the cotter pin (see (4) above) must be removed after the bomb has been installed in the airplane. Should it. be necessary to disassemble the fuze from the bomb, the above steps will be carried out in the reverse order and the components restored to their original packings.

d. Functioning-(1) Released armed-When the bomb is released armed, the arming wire is withdrawn from the fuze, thereby permitting the arming vane to be rotated by the air stream. The rotating arming vane, acting through the reduction gear train, unscrews the arming screw which carries the vane cup with it. This movement of the vane cup uncovers the arming disks which are then ejected by a spring. The striker carrying the firing pin is restrained from striking the primers only by the shear pin and setting pin which acts as a second shear pin. When the arming screw and vane cup are unscrewed, the arming stem is free to move forward to one of the two positions determined by the setting pin, instantaneous or delay. This movement of the arming stem determines the position to which the slider carrying the detonator moves, the movement being such as to bring the detonator in line for the action for which the fuze is set. On impact., both firing pins are driven in. The action which follows depends on the position of the slider (setting of the pin). If the setting is for delay action, the firing pin for instantaneous action strikes an empty cavity and, therefore, does not affect the delay action. On the other hand, if the fuze setting is for instantaneous action (detonator has moved to its position in line with the instantaneous firing pin), the instantaneous firing pin strikes its primer, thereby initiating instantaneous action.

(2) Released safe.-If the bomb is released safe, the arming wire is released from the arming mechanism of the bomb rack and drops with the bomb, thereby preventing the fuze from arming. Being unarmed, the fuze does not function on impact.

76. Fuze, bomb, M106 (tail).-a. General-This fuze is of the arming pin type, designed for delay action of approximately 45 seconds. It is used in the following demolition bombs :

(1) 100-pound, M30.

(2) 100-pound, Mk.IMIV.

(3) 300-pound, M31.

(4) 300-pound, Mk.IMII.

(5) 500-pound, M43.

(6) 600-pound, M32.

(7) 600-pound, Mk.IMII.

(8) 1,000-pound, M44.

(9) 1,100-pound, M33.

(10) 1,100-pound, Mk.IIIMI.

(11) 2,000-pound, M34.

b. Dcscription. (fig. 13).-The primer, delay element, and detonator are located in the body of the fuze. The delay of 45 seconds in this fuze is obtained by means of a coiled length of safety fuze incorporated in the explosive train between the primer and detonator. The firing pin is located in the tail end of the fuze and is restrained from moving by the arming pin. A creep spring, between the firing pin and primer, prevents the firing pin from creeping forward and resting on the primer after the bomb has been released from the airplane. The arming pin has two holes, the outer one for a cotter pin for shipment, the inner one which is visible only when a slight pressure is exerted on the head of the arming pin, is for the arming wire. The fuze is approximately 9.4 inches long over all. A similar but longer fuze for use in the 2,000-pound bombs for the Mk.-series is the fuze, bomb, M106, long (tail).

c. Assembly and disassembly (fuzing and unfuzing).-No attempt will be made to disassemble the fuze. The only authorized assembling operations are those required to assemble the bomb to the fuze and the arming wire to the fuze as described below.

(1) Remove fuze from sealed metal container.

(2) Screw fuze into the tail of the bomb until it seats-handtight, using no tools.

(3) See that split end of cotter pin in the arming pin points toward the nose of the bomb. This is to facilitate removal as well as insure that when it is later withdrawn, there will be no possibility of accidentally withdrawing the arming wire from the arming pin.

(4) Thread the longer end of the arming wire assembly through the rear suspension lug of the bomb and then through the inner of the two holes in the arming pin. A slight pressure on the head of the arming pin exposes the inner hole. The arming pin will not always be in line with the suspension lugs of the bomb. Care will be exercised that the arming wire is not wrapped around the fuze-the most direct line from the rear suspension lug to the hole in the arming pin will be followed.

(5) Adjust arming wire to protrude beyond arming pin from 2 to 3 inches. No safety clip will be used and the cotter pin must remain in its place. The fuze is now completely assembled to the bomb except that when the bomb is installed in the airplane, the cotter pin will be withdrawn, care being exercised that the arming wire is not disturbed.

d. Functioning.-(1) Released armed.-When the bomb is released with the fuze armed to detonate on impact, the swivel loop of the arming wire is held in the arming mechanism of the bomb rack, thereby causing the arming wire to be withdrawn from the fuze as the bomb drops. When the arming wire is withdrawn, the arming pin is ejected. The fuze is then armed and the firing pin is free to move toward the primer, being restrained only by a creep spring. On impact, inertia of the firing pin causes it to move forward, firing the primer.

(2) Released safe.-If the bomb is released safe, the arming wire is released from the arming mechanism of the bomb rack and drops with the bomb, thereby preventing the fuze from arming. Being unarmed, the fuze does not function on impact.

77. Bomb, demolition, 100-pound, Mk.IMIV.-a. General.-This bomb is of the "streamlined" type, as all other bombs of the Mk.-series with the exception of the 2,000-pound size. All components, such as fuzes, arming wire assemblies, etc., used with this bomb, are identical throughout the whole series, with the exception of the 2,000-pound size which uses an M106 long tail fuze instead of the standard M106 tail fuze. For the standard complete round assembly, the following components are required :

(1) Bomb, demolition, 100-pound, Mk.IMIV, unfuzed.

(2) Fuze, bomb, M105 (nose).

(3) Fuze, bomb, M106 (tail).

(4) Wire, arming, assembly.

b. Description.-This bomb is obtained by modification of the bomb, demolition, 100-pound. Mk.IMI, Mk.IMII, or Mk.IMIII. It contains approximately 66 pounds of high explosive and is adapted for both a nose and a tail fuze. To keep the fuze cavities free of foreign matter, a closing plug is fitted to the nose adapter opening and a closing tube assembly to the tail adapter opening. The box type fin, is attached to the tail end of the bomb by means of a fin lock nut.

c. Assembly and disassembly (fuzing and unfuzing).-The prior examination of components prescribed in paragraph 69 is for the purpose of insuring that all components at the bomb fuzing point are serviceable. The standard complete round is assembled as previously described.

(1) Tail fuze-After removing the tail closing tube assembly, assemble the tail fuze as prescribed in paragraph 69. Tighten fin lock nut if necessary.

(2) Nose fuze.-After removing the nose closing plug, assemble the nose fuze as prescribed in paragraph 69. The bomb is now an assembled complete round ready for installation in the bomb rack.

NOTE.-After the bomb has been installed in the bomb rack, the safety cotter pins are to be removed from the fuzes in accordance with instructions on the tags attached thereto. Should it be necessary to disassemble the complete round into its components, the above steps will be carried out in the reverse order and the components restored to their original condition and packings.

78. Fuze, bomb, M105 (nose).-a. General.-This fuze (fig. 14) is a selective, instantaneous, and short delay, arming vane type of fuze, in which the primer and the detonator are made an integral part thereof. It is provided with a mechanical delay arming mechanism, similar to that of the fuze, bomb, M103 (nose). The fuze may be set for either instantaneous or short delay action by means of a setting pin which projects from the side of the body. When shipped, the pin is in the deep slot or delay position. To set for instantaneous action, lift the pin, rotate one quarter turn, and drop it into the shallow slot. This fuze is used in the following demolition bombs :

(1) 100-pound, Mk.IMIV.

(2) 300-pound, Mk.IMII.

(3) 600-pound, Mk.IMII.

(4) 1,100-pound, Mk.IIIMI.

(5) 2,000-pound, Mk.IMIII.

(6) 2,000-pound, Mk.IMIV.

(7) 2,000-pound, Mk.IMV.

b. Description (fig. 14).-The selective action of this fuze is obtained by the use of two firing systems, one for instantaneous action, the other for delay. The detonator is housed in the base of the fuze. The delay action primer is fixed and always in position for delay action. The instantaneous action primer is moved into or out of its position for this action by the setting pin. When the setting pin is set "Inst." the primer is in position for instantaneous action. For the bombs in which this fuze is used, the booster is in the bomb as issued. The mechanical delay arming mechanism, arming disks, arming vane assembly, and vane strap are similar to those' of the fuze, bomb, M103. The fuze may be set at will, instantaneous or delay, any time before the bomb is installed in the bomb rack, or in those airplanes where accessibility permits the fuze may be set while the airplane is in flight.

c. Assembly and disassembly (fuzing and unfuzing).-No at-tempt will be made to disassemble the fuze. The only authorized assembling operations are those required to assemble the fuze to the bomb as described in detail below.

(1) Remove fuze from sealed metal container.

(2) Cut and remove seal wire, complying with instructions on seal tag.

(3) Screw nose fuze, less vane assembly, into the nose of the bomb until it seats-handtight, using no tools.

(4) Thread the shorter end of the arming wire assembly through the front suspension lug of the bomb and through the nearer pair of eyelets. Should the nearer pair of eyelets be occupied by the cotter pin and tag, place a second cotter pin through the pair of eyelets diametrically opposite, before removing the original cotter pin.

This cotter pin is not to be removed finally until after the bomb is installed in the airplane. A tag attached to this cotter pin reads, "To be removed after bomb has been placed in dropping gear and arming wire inserted. If bomb is not dropped, replace pin before, removing arming wire."

(5) Adjust arming wire to protrude from 2 to 3 inches.

(6) Slip one safety clip over end of arming wire until it just touches the face of the vane strap.

(7) Slip vane over vane holder so that the heads of the two vane pins enter mating holes in the flange of the vane holder and the vane holder spring snaps into the groove on the vane holder. The fuze is now completely assembled to the bomb, except that the cotter pin must be removed after the bomb has been installed in the airplane. Should it be necessary to disassemble the fuze from the bomb, the above steps will be carried out in the reverse order and the components restored to their original packings. Prior to repacking, the fuze will be inspected and resealed.

d. Functioning-(1) Released armed.-See paragraph 76d(1). (2) Released safe-See paragraph 76d(2).