Mk IV - The body consists of a hollow steel casting open at each end. The nose end is internally threaded to house an exploder container, which is locked in position by a locking screw. The tail end is shaped to take the tail cone, and is provided with four equally spaced slots to locate the spring clips on the tail. A male base plate threads into the after end of the body and has two threaded holes to receive the transit base bolts.
Mk V - This bomb is externally the same as the Mk IV, but has a central exploder tube instead of the exploder pockets at either end. The fuzing is in the tail only, and the nose is closed by a nose plug which has a cross cut in the end, instead of a ring as in the Bombs Mk IV.
The 500-lb. Tail No. 2 Mk I differs from the 250-lb. Tail No. 2 Mk I only in the weight and dimensions. The tail assembly consists of a tail cone with a cylindrical tail strut attached to it by four fins. It is attached to the bomb body by four spring clips.
The 500-lb. Tail Assembly No. 26 Mk 1 is similar to the 500-lb. Tail No. 2 Mk 1, differing mainly in weight and dimensions. It is used on the 500-lb. G.P. Bombs Mk IV or Mk V when carried externally on high-speed fighter aircraft, or internally on fighter bombers of the Mosquito type. The tail and fins are shorter, and it has a two-bladed arming vane instead of the four-bladed arming vane used on the Tail No. 2 Mk 1.
The bomb has a single suspension lug slightly aft of center of gravity, and secured to it by four countersunk screws.
Bomb Mk 5 was manufactured to use up existing stocks of Pistols No. 17 (long delay), which are too long to fit into the Bomb Mk 4.
The Anti-Disturbance Fuze No. 845, formerly incorporated in the nose when the Tail Pistol No. 37 was used, is now obsolete.
Tail fins are usually painted red when a time pistol is used.
The Bomb Mk 6 is made in the US and uses fuzes manufactured there to British designs: Nose Fuze Mk 7, M3; Tail Fuze Mk 5, M1.
British Bombs - Designation and Classification
Nose, Antidisturbance, No. 845 Mk 1, No. 845 Mk 2, No. 845 Mk 3, No. 845 Mk 4
Pistol, Tail, No. 17 Mk 1, No. 17 Mk 2, No. 17 Mk 3
Pistol, Tail, No. 37 Mk 4, No. 37 Mk 4*, No. 37 Mk 4**, No. 37 Mk 5, No. 37 Mk 5*, No. 37 Mk 6
OP 1665, British Explosive Ordnance (1946)