Blockbuster bomb

A blockbuster bomb or cookie was any of several of the largest conventional bombs used in World War II by the Royal Air Force (RAF). The term blockbuster was originally a name coined by the press and referred to a bomb which had enough explosive power to destroy an entire street or large building through the effects of blast in conjunction with incendiary bombs.

The bombs then called Blockbusters were the RAF's HC (High Capacity) bombs. These bombs had especially thin casings that allowed them to contain approximately three-quarters of their weight in explosive, with a 4,000-pound bomb containing over 3,000 pounds (1,400 kg) of Amatol. Most General-purpose bombs (termed Medium Capacity—or MC—by the RAF) contained 50% explosive by weight, the rest being made up of the fragmentation bomb casing. Blockbusters got larger as the war progressed, from the original 4,000 pounds (1,800 kg) version, up to 12,000 pounds (5,400 kg).

The Mark I 4000 lb bomb was a welded, cylindrical shell, made of 0.31-inch (7.9 mm) thick steel. The body of the bomb was 30 inches (76 cm) in diameter and 88 inches (2.2 m) long with a total overall length of 115 inches. The nose of the bomb was conical and a 27-inch (69 cm) long cylindrical tail was fitted (a lightweight, empty cylinder with a closed end). A T-section steel beam was welded to the inner surface of the bomb to strengthen it. Subsequent Mark II and Mark III HC bombs differed in detail; the conical nose was replaced with a domed nose and the number of fuzes was increased from one to three, in order to guarantee detonation. The Mark IV bomb did not have the T-section beam. The Mark V and Mark VI bombs were versions manufactured in the United States.

The larger 8,000 lb bomb was constructed from two 4,000 lb sections that fitted together with bolts, although these sections were of a larger 38 in (97 cm) diameter. A 12,000 lb version was created by adding a third 4,000 lb section.

The 4,000 lb high capacity design was little more than a cylinder full of explosives—it was unaerodynamic and did not have fins. The same weight American 4,000 lb (1.81 tonne) AN-M56 general purpose bomb was aerodynamically designed as its others were, with a sheet metal tailfin assembly and shaped nose and aft sections. When fitted with a nose spoiler and a drum tail the British "blockbuster" bomb fell straight. These bombs were designed for their blast effect, to cause damage to buildings - specifically to blow roof tiles off, so that the smaller 4 lb (1.8 kg) incendiary bombs could reach the building interiors. These high capacity bombs were used only by the RAF, being too big to fit in the bomb bays of other aircraft.

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