British Bomb, 250 lb Buoyancy, Mk 4
The bomb consists of a truncated, cone-shaped charge case with a concave nose welded on, a buoyancy chamber secured to the charge case by twelve nuts, and a clip-on tail. A convex nose attachment can be fitted to the nose by means of three brackets, equispaced around the edge of the nose. The buoyancy chamber has twelve hand clearance pockets around the forward end to permit access to the twelve bolts securing the charge case. Internal reinforcements are spot welded to the interior forward half of the buoyancy chamber, and two circular stiffeners extend athwartships through the chamber, spot welded to the chamber wall. An exploder tube extends centrally through the buoyancy chamber and charge case. It is welded at the rear to the joint ring fitting inside the fuze pocket, and supported by the stiffening ring in the middle of the buoyancy chamber.
The Tail No. 23 Mk I, used on the Mk III body, consists of a tail cone with cylindrical strut secured by four fins riveted to the strut and tack welded to the tail cone. The tail assembly is attached to the body by spring clips, and breaks free on water impact.
The bomb is suspended by a single lug secured by four screws threaded into a suspension-lug stiffener, and a boss, spot welded to the interior of the buoyancy chamber.
This bomb is designed to be dropped in front of ships under way, and to rise and detonate on contact with the ship’s bottom. The concave nose portion of this bomb is designed to give better underwater ballistics, rather than a Munroe effect.