W78
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The W-78 thermonuclear warhead is the warhead used on most of the US LGM-30G Minuteman III ICBM, along with the Mk-12A reentry vehicle which carried the warhead. Minuteman III's initially deployed with the older W62 warhead, the W-78 was deployed starting in December 1979 onto 300 missiles, 3 warheads per missile. Declassified US records indicate a total of 1,083 W-78s were produced.
The W-78 was designed at Los Alamos National Laboratory starting in 1974. The design is thought to combine the secondary (fusion) stage design of older ICBM warheads such as the W50 with a more modern primary stage (see Teller-Ulam design for more details).
The W-78 has a publicly announced yield of 335-350 kilotons.
Dimensions of the W-78 are unknown, but it fits within the Mk-12A reentry vehicle, which is conically shaped, 21.3 inches in diameter at its base and 71.3 inches long. The W-78 is estimated to weigh 7-800 pounds.
The W-78 does not use Insensitive High Explosives (explosives primarily based on TATB, which is very resistant to accidental detonation due to shock or fire or impact). As a result, it is considered a somewhat dangerous warhead, and cannot be transported by air unless there is no other safe option.
