3-in. Aircraft Rocket (Service)

Over-all length

Diameter

Total weight

Fuzing

Filling

Filling weight

Solid shot

25 lb. A.P. and S.A.P. Mk I

25 lb. A.P. Mk II

Over-all length

Diameter

Total weight

25.0 lb.

24.75 lb.

Over-all length

Diameter

Width of fins

Total weight

Burning time at 60° F.

Propellant

Porpellant weight

Mk I, 12.6 lb.; Mks II and III, 11.3 lb.

General: This is a aircraft rocket weapon, designed primarily for use against subma-rines and merchant shipping, although more recently wide use of the rocket has been made against land targets of an unarmored or lightly armored nature. The round consists of a 3-in. aircraft rocket, motor and one of the five following heads: Shell, H.E., 60-lb., F., No. 1 Mk I; Shell, H.E., 60-lb., S.A.P., No. 1 Mk I (with delay); Shell, H.E., 60-lb., S.A.P., No. 2 Mk I (wihtout delay); Shot, 25-lb., S.A.P., Mk I; Shot, 25-lb., A.P., Mk I; and Shot, 25-lb., A.P., Mk II. In addition, two concrete practice heads are also used, one weighing 25 lb, the other 60 lb.

Description

Shell, H.E., 60-lb., F., No. 1 Mk I – This shell has been manufactured by modifying a 4.5-inch Howitzer shell. The nose of the shell is recessed and internally threaded to re-ceive the nose fuze, while the base portion carries a threaded spigot for attachment to the shell ring of the rocket motor. The shell is painted dark green over-all, with the de-signation stencilled in ½-in. yellow letters around the shell body.

Shell, H.E., 60-lb., S.A.P., Nos. 1 and 2 Mk I – This shell consists of a cylindrical steel body internally threaded to receive a heavy steel ogival nose cap. The after portion of the body is internally threaded to receive a spigot, by which the shell is attached to the shell ring of the rocket motor. In the spigot are carried a gunpowder thermal initiator and a base fuze, beneath which is located a C.E. booster pellet. The shell is painted green over-all, with a ½-in. white and a ½-in. red band near the nose. A 1-in. light green band is painted around the shell body, and on this band are stencilled the initials of the explo-sive main filling.

The Head No. 1 Mk I employs the Fuze No. 865 Mk I (with delay) and the No. 2 Mk I uses the Fuze No. 878 Mk I (without delay). This is the only difference in the two shells.

Shot, 25-lb., S.A.P., Mk I – This is a solid steel shot. The nose portion of the shot is ogival, while the after portion terminates in a threaded spigot of reduced diameter, which screws into the shell ring of the rocket motor. The shot is painted black over-all, except for the nose end, which is painted white for a distance of one inch.

Shot, 25-lb., A.P., Mk I – Externally this shot appears identical to the S.A.P. shot. The nose portion is ogival, and the after body consists of a threaded spigot of reduced dia-meter, which screws into the shell ring of the motor. This spigot, in the case of the A.P. shot, is a separate component screwing into the internally threaded base portion of the shot. The spigot is held in place by a locking pin or a set-screw, which pierces the spigot and engages the shell body. The shot is painted black over-all, but carries a ½-in. white band in addition to the 1-in. white tip on the nose.

Shell, 25-lb., A.P., Mk II – This shot consists of a solid steel body machined externally to form a double ogive. This contour is considered to result in greater penetration and better underwater ballistics. Penetration is also enhanced by heat-treating the body of the shot. The after end of the body is recessed to form an empty cavity, and the base of this cavity is closed by a threaded spigot which screws into the shell ring of the ro-cket motor. The shot is painted black over-all, with a 1-in. white tip, and a ½-in. white band on the nose.

Shot, 60-lb., Practice (Concrete), Mk I – This is a blunt-nosed cylindrical head consis-ting of an adapter, externally threaded to screw into the shell ring of the motor and fit-ted with eight steel reinforced rods, welded into place. The concrete is the formed around the reinforced rods and shaped to measure 20 inches over-all and 6 inches in dia-meter.

Shell, 25-lb., Practice (Concrete), Mk I – This shell is manufactured in an identical manner to the 60-lb. Practice Shell, but measures only 11.5 inches in length and 5 inches in diameter.

Motor, Rocket, A/C, 3-in. No. 1 Mk I – This motor conists of a long steel cylinder with a shell ring at the forward end held in place by eight locking pins, which are held in en-gagement by two circular band spring. A thin metal-headed obtruator is located beneath the shell ring and is separated by cardboard washers from the forward end of the propel-lant grain. The head of the grain is castellated to accommodate the Igniter, Fuze, Elec-tric, No. 53*. The base of the propellant grain is supported by a metal grid, which in turn rests against the tail obtruator. The steel venturi tube is welded to the inside of the mo-tor just behind the tail obtruator and contains a bag of silica gel as a moisture-proofing measure.

The igniter leads extend from the igniter through the central annulus of the tubular cordite grain, along the outside groove of the cruciform grain in the Motors No. 1 Mks II and III. through the tail obruator and venturi, and through the metal closing plate, and terminates in a two-pronged plug. This plug connects with a socket extension on the rail launcher, when the rocket is loaded aboard the plaine.

Eight slots are located in the motor body near the after end for attachment of the four fins. The rocket are suspended by two saddles, each carrying a T-lug, which rides in the grooves of the launcher rails.

Motor, Rocket, A/C, 3-in., No. 1 Mk II – This motor differs from the No. 1 Mk I in that the propellant grain is cruciform in shape rather than tubular. The igniter leads are brought along the outside grooves of the grain, rather than through a central annulus, and a different type grid is employed. Proposed new nomenclature for the Motor No. 1 Mk II is: Motor, Rocket, A/C, 3-in., No. 5 Mk I.

Motor, Rocket, A/C, 3-in. No. 1 Mk III – The main difference between, the Motors Mk II and Mk III is that the Mk III has a weak link pigtail as against a niphon plug in the Mk II motor. The proposed new nomenclature for this motor is Motor, Rocket, A/C, 3-in., No. 5 Mk II.

Motor, Rocket, A/C, 3-in., No. 1 Mk IV – This motor differs from the No. 1 Mk III in that a small metal clip is loosely inserted over the igniter leads between the niphon plug and the attachment to the metal closing disc. The Motor Mk IV also has a longer pigtail lead; this greater length of lead being required for the lower round when using the "tier carriage" scheme. The proposed new nomenclature for this motor is Motor, Rocket, A/C, 3-in., No. 5 Mk II.

Remarks: These motors are colored either green ot white over-all, which identifica-tion stencillings in yellow.