W56

W56
Technicians work on the W56 Mk-11 warhead of an LGM-30F Minuteman II intercontinental ballistic missile.
Type	Nuclear warhead
Service history
In service	1963-1993
Used by	United States
Production history
Designer	Lawrence Livermore National Laboratory
Designed	1959 to 1963
Produced	March 1963 to May 1969.
No. built	1000
Specifications
Mass	600 pounds (270 kg) sans RV
Length	47.3 inches (1,200 mm) sans RV
Diameter	17.4 inches (440 mm) sans RV
Detonation mechanism	Contact, airburst
Blast yield	1,200 kilotonnes of TNT (5,000 TJ)

The W56 (originally called the Mark 56) was an American thermonuclear warhead produced starting in 1963 which saw service until 1993, on the Minuteman I and II ICBMs.

The warhead had a yield of 1.2 megatonnes of TNT (5.0 PJ) and a demonstrated yield-to-weight ratio of 4.96 kilotonnes of TNT per kilogram (20.8 petajoules per tonne), very close to the predicted 5.1 kilotonne of TNT/kg (21 PJ/t) achievable in the highest yield to weight weapon ever built, the 25 megatonnes of TNT (100 PJ) B41. However unlike the B41, which was never tested at full yield, the W56 demonstrated its efficiency in the XW-56-X2 Bluestone shot of Operation Dominic in 1962.^[1]

Production of the Mod 1 warhead began in March 1963. The Mod 4 warhead began production in May 1967 and finished production in May 1969. 1,000 total were produced, of which 455 were Mod 4 warheads. The warheads were retired between 1991 and 1993,^[2][3] and the last W56 warhead was dismantled in June 2006.^[4] During dismantlement, one warhead which had high-performance but sensitive polymer-bonded explosive in its explosive lenses is reported to have nearly detonated in 2005 when an unsafe amount of pressure was applied to the explosive while it was being disassembled.^[5]