A blockbuster bomb or cookie was one 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. Design 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 4000 lb bomb (nominal weight) containing about of explosive (Amatol, RDX or Torpex). Most general-purpose bombs, termed "medium capacity'" (MC) by the RAF, contained 50% explosive by weight, the rest being made up of the fragmentation casing. Larger Blockbusters were made later in the war, from the original version, up to . The 4000 lb High Capacity Mark I bomb – actual weight around – was a welded, cylindrical shell of thick steel. The body of the bomb was in diameter and long. The nose of the bomb was conical and a long lightweight, empty cylindrical tail with a closed end was fitted, for a total overall length of . 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 to guarantee detonation. The Mark IV bomb did not have the T-section beam and the Mark V and Mark VI bombs were versions manufactured in the United States. The larger bomb was constructed from two sections, of a larger diameter, that fitted together with bolts. A version was created by adding a third 4000 lb section and should not be confused with the 12,000lb Tallboy ground-penetrating "earthquake" bomb. The 4000-lb high-capacity design was little more than a cylinder full of explosives: it was unaerodynamic and did not have fins. By comparison the similar American "4,000 pound LC Bomb AN-M56" bomb was aerodynamically designed as other US bombs were, with a sheet metal tailfin assembly and shaped nose and aft sections. When fitted with a conical "nose piece" and a drum tail, the British "Blockbuster" bomb fell straight down. These bombs were designed for their blast effect,