The Mark 5 nuclear bomb and W5 nuclear warhead were a common core American nuclear weapon design, designed in the early 1950s and which saw service from 1952 to 1963.

Description

The Mark 5 design was the first production American nuclear weapon which, with a diameter of 39 in, was significantly smaller than the 60 in diameter implosion system of the 1945 Fat Man nuclear bomb design. The Mark 5 design used a 92-point implosion system and a composite uranium/plutonium fissile material core or pit. The Mark 5 core and W5 warhead were 39 in in diameter and 76 in long; the total Mark 5 bomb had a diameter of 44 in and was 129-132 in long. The different versions of Mark 5 weighed 3025-3175 lb; the W5 versions weighed 2,405-2,650 lb. The Mark 5 and W5 were pure fission weapons. There were at least four basic models of core design used, capable of compatibility with at least eight different core "capsule" designs (which themselves were compatible with many other weapons of the era). Sub-variants with yields of 6, 16, 55, 60, 100, and 120 kilotons have been reported. As with many early US nuclear weapon designs, the fissile material or pit could be kept separately from the bomb and assembled into it during flight. This technology is known as In Flight Insertion (IFI). The Mark 5 had an automatic IFI mechanism which could insert the pit into the center of the explosive assembly from a storage position in the bomb nose.

History

The Mark 5 was in service from 1952 to 1963. The W5 saw service from 1954 to 1963. Approximately 72 Mark 5 weapons were supplied for delivery by Royal Air Force bombers but under US control, under the auspices of Project E. A Mark 5 was used as the primary fission trigger used in Ivy Mike, the first thermonuclear device in history. A total of 140 Mark-5 bombs were produced.