ALLIED BOMBS AND FUZES

BRITISH AIRCRAFT BOMB FUZES

I. General Notes.

A. British fuzes are diveded into two main classifications. If the "fuze" does not con-tain any explosive components when it is normally shipped or issued, the British use the term PISTOL. A Pistol, thereforce will never contain a primer, detonator or booster as an integral part. Examples of British Pistols are Tail Pistol No. 28 (File 2211.T4) and Nose Pistol No. 45 Mk. I (File 2212. N10). No primer or detonator is found in the Pistols.

B. The term "FUZE" is applied to any Pistol in which a primer-detonator is an integral part. In most cases, a bursting charge or booster is attached. Examples of British Fuzes are Nose Fuze No. 845 Mk I (File 2225.N10) and Tail Fuze No. 848 Mk I (File 2214.T20).

C. The nose pistols depend for their action on a pressure plate attached to the up-per end of a plunger, the lower end of the plunger being tapered to form the striker. On impact, this plate forces the plunger inwards, causing the striker to detonate the cap in the cartridge head of the detonator.

D. The tail pistols depend for their operation on an inertia weight, the lower end of which is tapered to form the striker. The inertia weight is locked in position during tran-sit by the arming vane nut and a creep spring. When the safety wires are withdrawn and the bomb is released, the arming vanes rotate to unscrew the arming vane nut and only the creep spring prevents the striker from hitting the cap. On impact, the inertia weight compresses the spring and allows the striker to fire the cap in the cartridge head of the detonator.

E. The nose fuzes are generally used for instantaneous action while the tail fuze are generally used for delay action. In the British method of selective fuzing which is opera-ted by electrical means, the safety wire may be removed from either the nose fuze or the tail fuze or both, thus determining which fuze are to be armed. This permite the bombardier to make a choice between instantaneous or delay action.

II. Types of Safety Devices.

Any of the follwing safety devices may be fitted to an Aircraft Bomb Fuze:

A. Safety Pin – This is a split pin which passes either through the plunger or through the inertia weight and prevents their movement in either direction. It is removed imme-diately prior to flight.

B. Shearing Wire – This is a plain cylindrical wire and is fitted to nose fuze only. The thickness of the wire being the messure of the force required to shear it. It serves two purposes:

1. If the safety pin is removed, the plunger is still locked.

2. If the bomb strikes a light obstruction, such as the branch of a tree, etc., the shearing wire prevents the fuze from operating.

C. Arming Vanes – These are permanently attached to the arming vane nut, or dome, which is screwed onto the plunger or inertia weight and so prevents movement of the striker until the bomb has fallen some distance.

D. Arming Vane Stops – These are fitted to the bomb carrier or to the bomb fuze, depending on the type, and prevent the rotation and consequent loss of the arming va-nes during the flight of the aircraft. They, therefore, serve to retain the fuze in a safe condition.

E. Pressure Plate Stop – This is fitted between the pressure plate of the nose fuze and the body: it prevents the pressure plate, plunger and striker from being driven into the bomb when the fuze is dropped "safe".

F. Fuzing Wires – These are fitted to the bomb carrier and form the meane of fuzing the bomb as "safe" or "live" on release.

G. Red Ring on striker Pellet – This indicates the position of the striker pellet in the body of the tail fuze, or the position of the arming vanes spindle in the pressure plate of the nose fuze.

H. Green Spring – This is fitted in tail fuzes to hold the striker away from the deto-nator cap when the arming vanes have come off during the fall of the bomb.

III. Types of Threads Used on Bomb Fuzes.

The following body threads are employed in the construction of noses and tail fuzes:

A. Nose Fuze Body Threads.

1. Admiralty taper.

2. Standard parallel.

B. Tail Fuze Body Threads

1. Standard parallel (1.375 inches or 1.1 inches diameter).

Note: Certain bombs have a larger diameter internal threads at the tail end than that of the tail fuzes; therefore in these bombs it is necessary to use Adapter Fuze Bomb, 1.375 inches, in conjunction with the fuze.

IV. Anti-Withdrawl.

An anti-withdrawl device is fitted on the tail pistols No. 37, Mk III and Mk IV and the No. 17 Mk I and II. They are the only pistols which incorporate an anti-withdrawl device at the present time.

V. Anti-Disturbance.

The Nose Fuzes No. 845 Mk I and II are the only anti-disturbance fuzes which are used at the present time. New anti-disturbance fuzes are under development.