GENERAL:

The development of rocket-type ammunition was begun by the British several years prior to the entrace of Great Britain into World War II. As early as 1936 experiments were begun in the field of rocketry. It was felt that, though experimentation should proceed in all types of rocket weapons, the development of a satisfactory anti-aircraft weapon should be given the greatest emphasis. Anti-aircraft rockets, though far less accurate than artillery, non the less were inexpensively made and could be manufactured in quan-tities sufficient to allow complete saturation of a defensive area.

Accordingly, in 1940 when the German "blitz" began, two anti-aircraft rocket weapons were introduced into service use, the 2" U.P. (2-inch "Unrotated Projectile") and the 3" U.P. These consisted of high explosive heads fitted to a standard type, fin-stabilized rocket motor, and fuzed with impact or pyrotechnic aerial burst fuzes.

At about the same time, a 5" Chemical rocket, the 5" U.P., was adopted for land ser-vice use. The rocket proved to have few profitable uses and was turned over to the Bri-tish Navy. The Navy manufactured a high explosive, a smoke, and an incendiary shell for the rocket, mounted the launcher on a converted landing craft, and used it for beach barrage purposes, christening it the "Sea Matress".

Not much later, a noval type anti-aircraft defense was developed in the "Wire Bar-rage" or "Aerial Mine Field" apparatus. This device was propelled or towed by a standard rocket motor. Its function was to suspend from a parachute a steel cable or a long length of piano wire with a small H.E. bomb attached. The apparatus served to break up an aircraft, if it struck the wire or cable, or to cause the aircraft to take evasive action and thus leave its target run. This type of apparatus was found to be particularly effec-tive for defense of merchant ships against low-level or dive-bombing aircraft.

Developments in other fields of rocketry included aircraft rockets for attacks against armored vehicles, merchant shipping, and submarines. More recently an assault rocket for infantry use and a land barrage rocket, designed as a medium range artillery support weapon, have been introduced.

STABILIZATION:

Though all British service rockets are designed solely for fin stabilization, more recent types incorporate fins of greatly reduced surface. To decrease the amount of dispersion caused by venturi variations, spiral rails have been fitted to the inside of the launcher barrel. The short fins engage these rails and impart a spin of about 800-900 r.p.m. to the rocket. However, this is not spin-stabilization in the accepted sens ot the term.

PROPELLANT:

The British rocket program was aided in its early stages by the ready availability in large quantities of a good and relatively inexpensive rocket propellant. The British have long employed a type of cordite as their principal projectile propellant charge, and sol-ventless extruded cordite proved remarkably adaptable to rocket use. Solventless cor-dite, identified by the code letters "S.U.", is a double base powder consisting of 41.5% nitroglycerine, 49.5% nitrocellulose, and 9.0% carbamite, as stabilizer. Flashless cordite is obtained by adding potassium cryolite. Flashless charges are identified by the symbol "/K." added to the propellant code letters.

Several different propellant shapes have been designed by the British always in an attempt to gain the most efficient burning of the propellant. The charge shapes and identifying symbols are as follows:

PROPELLANT SHAPE

Tubular, drilled

/D.

Tubular, slotted

/S.

Tubular, slotted & grooved

/S.G.

Cruciform

/X.

Cogged

/C.

These code letters and symbols will be found stencilled on all rocket motors, ginving a complete description of the propellant grain used. Thus the letters "S.U./K./X." would in-dicated a cruciform grain of flashless solventless cordite; the letters "S.U./S.G.", a tubu-lar grain of solventless cordite, slotted and grooved; etc.

The standard ignition mechanism for British rockets consists of an electric squib (Fuze, Electric, No. F 53), inserted in a paper tube or metal cylinder, which also can con-tains a quantity of igniting composition. The composition comprises magnesium, potass-ium nitrate, and a small amount of acaroid resin as a stabilizer. The igniter is generally fitted into castellations out in the head of the propellant grain.