British Bomb, 25 lb Practice, Mk 1, Mk 3, Mk 4, Mk 5
This bomb consists of a solid, cast-iron nose section bored centrally to house a striker head, to which are attached a long striker rod and striker. A striker guide bush is threaded into the after end of the central bore. A shear wire through the guide bush and the striker prevents the striker from contact with the detonator burster in the unarmed position. During transit and normal handling, the striker also is retained by a split pin and a spring-loaded safety pin. The split pin is removed when the bomb is loaded aboard the plane, and the safety pin is ejected when the bomb is released.
The tail consists of a long tail cone, closed at the wider end by a central plug. A central tube for the detonator burster passes through the tail cone. Located in the central plug, slightly off-center, is a filling plug through which the smoke or flash filling is inserted. As in most British practice bombs, the filling is contained in what is actually a part of the tail portion of the bomb. A tail tube is attached to the after end of the tail cone and supports a cylindrical shroud and four fins. The central plug is threaded externally and screws into the after end of the cast iron nose section of the bomb.
A single U-shaped suspension lug is provided to suspend this bomb.
The smoke filled bombs are used for daylight operations; the flash-filled at night. Because of their solid cast-iron noses, these bombs should not be used against lightly armored targets.
The Bombs Mk I and Mk III are identical, except for the fillings. The Mk IV, which replaces the Mk I, is similar to it in construction, but differs in the following respects: The safety plunger and transit safety pin have been increased in diameter. The plunger is retained by a flexible steel safety wire permanently attached to a safety collar which is threaded internally to accept the transit safety pin. The transit safety pin is screwed into the safety collar, thus retaining the assembly firmly until the bomb is on the carrier.
The Bomb Mk V which replaces the Mk III, is mechanically identical to the Mk IV, but differs in the filling.