The W40 nuclear warhead was an American nuclear warhead developed in the late 1950s and which saw service from 1959 to 1972. It was a fusion-boosted fission type weapon.
The W40 design was reportedly the common Python primary or fission core used by the US B28 nuclear bomb, W28 nuclear warhead, and W49 nuclear warhead.
The W40 was 18 inches in diameter, 32 inches long, and weighed around 385 pounds. It had a design yield of 10 kilotons.
The W40 was used in the MGM-18 Lacrosse surface to surface missile (SRBM) and CIM-10 Bomarc surface to air missiles (SAM).
The Bomarc warhead was lethal to a medium bomber aircraft in about one kilometer distance. The warheads were mounted to the missiles for 90 day intervals, after which they underwent periodic inspection and maintenance.
The first production device was made in January 1959, with production starting in June, withdrawal in August due to a significant safety issue, and re-release in September with a temporary fix. An one-point safety problem was discovered in 1960, and a W40 mod 2 with a fix was developed later and sent out in December 1963.