The main explosive in aircraft bombs is relatively insensitive and to effect detonation a train of more sensitive explosives is normally used. The explosive train in British bombs may be either of two types:

(a) The fuze-exploder-main charge type.

(b) The pistol-detonator-exploder-main charge type.

The distinction between fuzes and pistols has been made in the introductions to both fuzes and pistols, but, to repeat briefly, fuzes have the initiating explosive charge incorporated in them; whereas pistols contain no expolsive whatsoever, merely acting as a mechanical device to activate the initiating explosive in a detonator inserted sepa-rately in the bomb.

Bombs employing a pistol-detonator combination are generally shipped with the pistol in place without the detonator, which is inserted prior to loading on the plane after first removing the pistol. In small bombs (500 lbs. or under), the detonator generally fits into the exploder, whereas in larger bombs it is housed in a detonator holder which threads into the exploder container and is threaded itself to receive the pistol.

Detonators are of two types, the anvil type employed with pistols having a blunt striker, and the sensitive type employed with pistols having a needle striker. Further-more, they may be instantaneous in functioning, or may have a delay of from .025 sec. to 11 sec.

The most sensitive explosive in the pistol-detonator firing train is usually contained in a cap and is fired by impact or friction; the flash from the cap composition firing a less sensitive composition known as detonating composition, which in turn initiates a still less sensitive explosive called the exploder which initiates the main charge. Sensitive type detonators, however, have no percussion cap or anvil.

The composition usually used in British detonators is A.S.A. mixture, composed of lead azide and lead styphnate. Fulminate or mercury is also used. Formerly, C.E. (tetryl) and T.N.T. were used in the exploder, but the use of T.N.T. is being discontinued and C.E. alone is being used.