bomb, or, more recently, GPS-guided weapon (like the U.S. JDAM). The combination is cheaper than a true guided missile (and can be more easily upgraded or replaced in service), but is substantially more accurate than an unguided bomb. Historic GP bombs WWII-era British general-purpose bombs During WWII the British adopted a description of general-purpose bombs as medium capacity (MC) bombs. The MC was developed from 1942 to replace the existing 1000 lb GP (General Purpose) bomb. Initially using most of the components of the 1000 lb GP it was decided to give it a new tail and it was built with a half-inch-thick wall. Fillings could be Amatex, Amatol, Minol, RDX and others. Actual weight was around . It was introduced to service in 1943 and about a quarter of a million were produced by the end of the war. General-Purpose bomb – produced 1937 to 1941 General-Purpose Bomb – not produced General-Purpose Bomb – abandoned project General-Purpose Bomb (1926 onwards) – replaced by 250 lb MC in 1942 General-Purpose Bomb (1926 onwards) – replaced by 500 lb MC in 1942 General-Purpose Bomb (1939 onwards) – replaced by 1000 lb MC in 1943 General-Purpose Bomb (1941 onwards) General-Purpose Bomb (1943) – replaced by 4000 lb HC Modern GP bombs Modern American GP bombs: the Mark 80 series During the Korean War and Vietnam War the U.S. used older designs like the M65, M117 and M118, which had an explosive content about 65% higher than most contemporary weapons. Although some of these weapons remain in the U.S. arsenal, they are little used and the M117 is primarily carried only by the B-52 Stratofortress. The primary U.S. GP bombs are the Mark 80 series. This class of weapons uses a shape known as Aero 1A, designed by Ed Heinemann of Douglas Aircraft as the result of studies in 1946. It has a length-to-diameter ratio of about 8:1, and results in minimal drag for the carrier aircraft. The Mark 80 series was not used in combat until the Vietnam War, but has since replaced most earlier GP weapons. It includes four basic weapon types: Mark 81 – nominal weight Mark 82 – nominal weight Mark 83 – nominal weight Mark 84 – nominal weight Vietnam service showed the Mk 81 "Firecracker" to be insufficiently effective, and it was withdrawn from U.S. service. However, recently, precision-guided variants of the Mk 81 bomb have begun