American Projectiles and Explosives
Navy Rockets
7.2-inch H.E. "Mouse Trap" and 2.5-inch Practice
No picture available
Overall length: 38.6 inches
Head length: 19 inches
Head weight: 17.9 pounds
Wall thickness: 0.2 inches
Motor length: 15.9 inches
Motor diameter: 2.25 inches
Motor weight: 8.1 pounds
Tail width: 7 inches
Filler Weight (TNT): 31 pounds
Total weight: 65 pounds
General: This rocket was designed for use by patrol vessels against submarines. The most common installation consists of two four-rail Launchers Mk 20, with a fixed elevation of 48 degrees, mounted on the fore deck with firing controlled from the bridge.
Head: The projectile consists of a flat-nosed head with a conical tail fairing and parallel sides. The adapter and fuze thread into the nose, and the motor unit threads into the base.
Motor: The Motor Unit Mk 3 contains a long single pellet of smokeless powder which, when ignited by a black-powder primer fired by an electric squib, burns at a pressure of 1,000 to 2,500 pounds per square inch. The gases are forced out aft through the nozzle in the rear end of the motor tube. The burning continues for 0.2 to 0.7 seconds, during which time the missile travels about 30 feet. At this point, propulsion ceases and the projectile is free in flight. This projector charge is intended for use on the 7.2-inch Rocket Launchers Mk 20, Mk 21, or Mk 22.
Tail: A steel tube attached to the head by a threaded joint has fins with two circular drums attached to the after end. The vanes have a 10-degree twist to give a slow rotation and prevent ruddering. The two vane-support drums also act as contact rings, the wiring from the electric squib passing from the primer after to the two rings which serve as firing contacts.
Remarks: When Torpex is used, the weight is increased by approximately 2.5 pounds.
The 2.5-inch sub-caliber rocket, consisting of the 1.25-inch Motor Mk 1 and 2.5-inch Head Mk 1, is a miniature of the regular rocket and is used in practice. The motor contains a single tubular powder grain, an igniter, and lead wires. The tail fins, supported by a shroud, are offset five degrees to impart some rotation to the round, to improve underwater travel. The Head Mk 1 has a cavity for a shotgun shell; the Head Mod 2 Mk 1 is solid.
The Fuzes Mk 131 and Mk 140 are replaced by the Mk 156 in service rounds.
7.2-inch D.R., also T37 and T38
(Head Mk 10)
Overall length: 35 inches
Motor diameter: 2.25 inches
C-2 Explosive: 33 pounds
Loaded weight: 60 pounds
Maximum range: 275 yards
Motor: 2.25-inch Mk 3
Fuzes:
-Head Mk 5: Nose Fuze Mk 152 or Mk 141
-Head Mk 10: Base Fuze Mk 146
-Head Mk 10-1: Base Fuze Mk 161 Mod 0
General: The 7.2-inch D.R., a modification of the 7.2-inch H.E., was used for demolition of anti-tank obstacles. The 7.2-inch D.R. was projected from a multiple-rail armored launcher mounted on the turret of the Tank M4. It was fired at point-blank range and proved effective against concrete obstacles at ranges of 100 to 150 feet.
Description: The rocket has a thin steel head to give the maximum blast effect. The propellant is the single unperforated cruciform Grain Mk 10. The body can be fitted with any one of a number of rocket motors to give velocities from 175 to 400 feet per second. The mean lateral deviation is 10 mils from a 90-inch launcher.
The Base Fuzes Mk 146 and Mk 161 Mod 0 are armed during flight by the pressure of the gas evolved from the burning propellant acting on the diaphragm. The Head Mk 10 Mod 1 is the Head Mk 10, slightly altered to accommodate the new motor adapter of the Base Fuze Mk 161 Mod 0.
Remarks: The Army designates the Head Mk 10 or Mk 10 Mod 1 as the T37.
A smoke-filled round used by the Army is the same size, and has the designation of T38. It is nose-fuzed with either the Fuze Mk 152 or the Fuze Mk 141.
The Head Mk 5 may take either the Booster Mk 1 or the Booster Mk 2; the Head Mk 10, only the Booster Mk 1.
The Heads Mk 5 are loaded with TNT; the Heads Mk 10 may also take a TNT load.
7.2-inch C.W.R.N. and M25, M27, and T24
(Motor Mk 5 and Head Mk 7)
Overall length: 48.1 inches
Head width: 7.2 inches
Head length: 18.75 inches
Motor length: 29 inches
Propellant (ballistite): Grain Mk 11
Filler: Any chemical filler with specific gravity over 1.2
Filler (F.S.): 19.7 pounds
Total weight: 53.2 pounds
Range: 3,500 yards
Fuzes: Nose Mk 147 or Mk 147 Mod 1
General: This rocket is fired from a 24-rail demountable, variable-elevation launcher carried in a 2 and 1/2 ton truck. The salvo is fired in 2.5 seconds, and the launcher can be reloaded in 1.5 minutes.
These rockets of Navy design are under production by the Army. The only essential difference between the rockets as used by the Army and the Navy is in the propellant.
Head: The container is a bulb-shaped steel tube open at both end. The adapter fits inside the flange on the forward end of the container and is brazed thereto. The wide forward end of the adapter is internally threaded to seat the fuze. The burster tube, made of steel, fits inside the adapter and extends downward into the container. The tube and adapter are held together by a press fit and sealed with white-lead paste. The rear end of the tube is closed.
Motor: The motor is a steel tube, with the forward end externally threaded to screw-into the connector of the head. The nozzle is slipped down through the open end of the motor body, and the end is welded to the inner edge of the motor-body rim.
Tail: The tail assembly has four tail vanes spot-welded in pairs to the motor tube and spot-welded to the rear shroud. The forward shroud is riveted to the vanes but insulated from them. Four large fins are welded to the motor tube, pass over the forward shroud, and are welded to the rear shroud. The lead wires are connected to the two shrouds which serve as contacts.
Propellant: As produced for the Navy, the propellant consists of a single grain of solvent-less extruded ballistite with an outer diameter of 2.5 inches and an inner diameter of 1 inch. This is the Grain Mk 11.
In the Army Chemical Rocket M25, the propellant consists of four sticks of ballistite, with a one-inch axial hole, placed end to end with separating washers between the sticks. The sticks are three-ridged, and each has eight sets of holes radially through it. The overall length of the sticks is 20.5 inches.
Remarks: The Army Rocket M27 is structurally the same as the Navy rocket, but is filled with C/K gas. Its total weight is 51.8 pounds.
A head similar tot he Mk 7 but loaded with 22 pounds of TNT and equipped with a booster instead of a burster tube is known as the Mk 9. It is a demolition head, using the Fuze Mk 137 and the 3.25-inch Motor Mk 5. This combination may be used to lay down a barrage from the same launchers as the C.W.R.N.
When the Head Mk 9 is fuzed with the Fuze Mk 147, it is known as the Round T24. Its total weight is 51.8 pounds.
11.75-inch A.R. "Tiny Tim"
Overall length: 123 inches
Total weight: 1,253 pounds
Head length: 47 inches
Head weight: 600 pounds
Motor length: 82.4 inches
TNT filling: 152.5 pounds
Fuzes:
-Mk 1 Mod 0: Mk 157 Mk 1
-Mk 1 Mod 1: Mk 157 Mod 2
-Mk 2 Mod 0: Mk 157 Mod 2, Mk 163 Mod 0, Mk 162 Mod 0
Heads: The Mk 1 Mod 0 consists of a standard 500 pound S.A.P. Bomb AN-M58A1 modified for this particular use. The changes include the removal of the suspension lugs, an increase in the number of threads securing the base plate, the use of a new base plug to take the Fuze Mk 157 Mod 1, and the use of an adapter ring welded around the after end as a means for attaching the rocket motor. The motor gases are sealed from the high explosive in the body by coating the threads of the base plate with a luting compound, and also by a gasket under the fuze body flange.
The Mk 1 Mod 1 is similar to the Mk 1 Mod 0, except that a projectile-type gas seal is added around the head of the Fuze Mk 157 Mod 2.
The Mk 2 Mod 0 was developed from the Mk 1 Mod 1. This head differs in that it has a solid-nosed "Common" head and a base plate modified to take three Base Fuzes Mk 157 Mod 2. The projectile-type gas seal is used around all fuzes and also between the base plate and the forged steel body. The Fuze Mk 157 Mod 2 is used with one Auxiliary Booster Mk 1 Mod 09, or the Fuze Mk 163 Mod 0 with one Auxiliary Booster Mk 19 Mod 0.
The Head Mk 3 Mod 1 was issued for practice to simulate the Head Mk 2 Mod 0.
The Head Mk 4 Mod 0 is slightly lighter and shorter than previous heads. The head weight is 578 pounds, including 152 pounds of TNT. The head length is 46 inches. Three Fuzes Mk 153 Mod 0 or Mk 162 Mod 0 are used in the base. The penetrative characteristics of this head are the same as those of rpesent types, but slightly better overall performance may be expected, because of the small increase in velocity resulting from reduction in total weight.
The Practice Head Mk 5 dummies the Mk 4. It is 44.75 inches long and weighs 569 pounds. It has a cavity for a smoke puff.
The heads are shipped loaded and fuzed. A cuff protects the threads on the adapter ring and the fuze during shipment.
Motors: The Mk 1 Mod 0 consists of a steel tube, the after end of which is threaded to receive a plate having twenty-five nozzles. The motor tube contains four propellant grains of solvent-less extruded ballistite of cruciform cross-section, weighing 147 pounds. The grains are shielded from each other by an X-shaped partition which extends longitudinally for almost the full length of the motor tube. The grains and the partition are supported by the grid and are strapped together by aluminum bands.
In normal operation, the gases from the burning powder do not pass through the central nozzle, which is closed by a copper blowout disc. Only when the pressure in the motor exceeds approximately 22,500 pounds per square inch is this disc expelled, bringing the central nozzle into operation. The use of a blowout disc allows the rocket motor to perform satisfactorily over a greater temperature range. It has one disadvantage, however, in that at motor temperatures of about 100 degrees Fahrenheit, where the normal operating pressure is just enough to shear the disc, it is impossible to predict whether it will blow out or not. If it does, the burning time is lengthened and the gravity drop is increased, so that the rocket may miss the target.
Four black-powder charges of about 0.5 pounds each, contained in plastic cases at the front ends of the grains, provide the ignition for the propellant. They are set off by two small electric squibs in each case, which are connected to receptacles in the nozzle plate. The burning of the propellant is markedly affected by its moisture content. Consequently, the motors are sealed at both ends. Each of the 24 peripheral nozzles is sealed with a thing steel cup. The front end is sealed with a thin steel disc having in its center a small blowout window. This window is blown out by the motor pressure, allowing the propellant gases free access to the base fuze. These closures should not be removed.
The Igniter Mk 19 Mod 0 has recently been developed for use in 11.75-inch A.R. motors. Known as a tin-plate case igniter, it consists of a single metal case 3.38 inches in diameter and 1.8 inches deep, with a wall thickness of 0.01 inches. Four clips are soldered to the base of the case, for attachment to the motor charge support. The case contains 230 grams of F.F.F.G. black powder. Contained in the case are two electric squibs connected in parallel to the igniter lead wires.
Motors must never be fired above the rated temperature stenciled on the motor, because they are likely to burst. Below the lower rated temperature, occasional ignition failures and interrupted burning may be experienced.
The Motor Mk 1 Mod 1 is identical to the Mk 1 Mod 0, except that the motor tube is of higher tensile strength and the pigtail connection has been replaced by two receptacles built into the base plate.
The Mk 1 Mod 2 is a design in which the dead space between the forward motor closure and the base of the rocket head has been eliminated. This motor is similar in other respects to the Mk 1 Mod 0, except that the overall length has been reduced to 75.75 inches by two receptacles built into the base plate.
The Motor Mk 1 Mod 3 is the Bureau of Ordnance production of the Mk 1 Mod 2.
The Motor Mk 2 Mod 0 weighs 600 pounds and is 72.04 inches in length. Length and weight reduction have been accomplished by improvements in design detail. so that the total amount of propellant in the motor has not been changed. Because of design and construction changes, the Motor Mk 2 Mod 0 may be used only with the Head Mk 4 Mod 0.
Next Time: Aircraft Pyrotechnics (Part 1)
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