HEAD: Mk 1 Mod 0; MOTOR: Mk 1 Mod 0

OVERALL LENGTH

TOTAL WEIGHT

HEAD DIAMETER

HEAD LENGTH

HEAD WEIGHT

WALL THICKNESS

MOTOR LENGTH

MOTOR DIAMETER

FILLING

WEIGHT OF FILLING

FUZES: Mk 1 Mod 0

Mk 1 Mod 1

Mk 2 Mod 0

Mk 157 Mod 0, Mk 163 Mod 0

ROCKET HEAD:

The Mk 1 Mod 0 (a CIT production) consists of a standard 500 lb. SAP AN-M58A1 bomb modified for this particular use. The changes include the removal of the suspen-sion lugs, increase in number of threads securing the base plate, use of a new base plug to take the Mk 157 Mod 1 fuze, and the use of an adapter ring welded around 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 a gasket under the fuze body flange.

The Mk 1 Mod 1 (a CIT production) is similar to the Mk 1 Mod 0 except a projectile type gas seal is added around the head of the fuze which is the Mk 157-2.

The Mk 2 Mod 0 (a BuOrd production) 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 Mk 157-2 base fuzes. The projectile type gas seal is used around all fuzes and also between the base plate and the forced steel body. The Mk 157-2 fuze is used with one Mk 1-0 auxiliary booster or the Mk 163-0 with one Mk 19-0 auxiliary booster.

The Mk 3 Mod 1 head was issued for practice to simulate the Mk 2-0.

The bodies are shipped loaded and fuzed. A cuff protects the threads on the adap-ter ring an the fuze during shipment.

ROCKET MOTOR:

The Mk 1 Mod 0 (a CIT production) 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 solventless extruded ballistite of cruciform cross-section, weighing 147 lbs. The grains are shielded from each other by an "X"-shaped partition which ex-tends longitudinally for almost the full length of the motor tube. The grains and the par-tition 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 shear disc (blowout disc). Only when the pressure in the motor exceeds approximately 2250 lb/in.² is this disc expelled, bringing the central nozzle into operation. The use of a blow-out disc allows the rocket motor to perform satisfactorily over a greater temperature range. It has one disadvantage, how-ever, in that at motor temperatures of about 100° F, where the normal operating pres-sure 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 lb. 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 receptables in the nozzle plate. The burning of the propellant is markedly affected by its moisture content. Con-sequently, the motors are sealed at both ends. Each of the 24 peripheral nozzles is sealed with a thin steel cup. The front end is sealed with a thin steel disc having in its center a small "blow-out window". This window is blown out by the motor pressure, thereby allowing the propellant gases free access to the base fuze. These closure should not be removed.

The igniter Mk 19 Mod 0 has recently been developed for use in 11.75" AR motors. Known as a tin-plate case iginter, it consists of a single metal case 3.38" in diameter and 1.8" deep, with a wall thickness of .01". Four clips are soldered to the base of the case, for attachment to the motor charge support. The case contain 230 grams of FFFG 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 stencilled on the motor be-cause they are likely to burst. Below the lower rated temperature, occasional failure and interrupted burning may be experience although none has been found in six rounds fired at -30° F.

The Mk 1 Mod 1 motor is the BuOrd production. This motor is identical to the Mk 1 Mod 0 except that the motor tube is of higher tensile strenght and the pigtail connect-ion has been replaced by two receptacles built in the base plate.

The Mk 1 Mod 2 motor is a CIT production 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 was redu-ced to 75.75 inches and the pigtail connection has been replaced by two receptacles built in the base plate.

The Mk 1 Mod 3 motor is the BuOrd production of the Mk 1 Mod 2.

REMARKS:

(1) C.I.T. refers to the California Institute of Technology which develops the rockets for the Bureau of Ordnance. As the rockets are adopted by BuOrd, new Mark or Mod numbers are assigned.