W25 (nuclear warhead)
The W25 was a small nuclear warhead developed by the United States Air Force and Los Alamos Scientific Laboratory for air-defense use. It was a fission device with a nominal yield of 1.5 kt. Development of the weapon began in 1954 at the behest of Douglas Aircraft for use against enemy bombers.
The W25 was used for the MB-1 "Ding Dong", an unguided air-to-air rocket used by the F-89 Scorpion, F-101B, and F-106 interceptor aircraft. The MB-1 entered service in 1957, and was eventually redesignated the AIR-2 Genie. The only non-U.S. user was Canada, whose CF-101 Voodoos carried Genies until 1984 via a dual-key nuclear sharing arrangement. Limited numbers were still used for Air National Guard F-106 aircraft until December 1984.
The W25 is 17.4 inches (44 cm) in diameter and 26.6 inches (68 cm) long, with a reported weight of 218-221 pounds (98.8 - 100.2 kg) .
The W25 was described as a composite pit (utilizing both Uranium and Plutonium), unboosted, and the first US sealed pit design. A sealed pit means that a solid metal barrier is formed around the pit or nuclear material components inside a nuclear weapon, with no openings. This protects the nuclear materials from environmental degradation and helps reduce the chances of their release in case of an accidental fire or minor explosion.
See also 
- W53 - the warhead used on the Titan II ICBM
- W54 - very small yield warhead, one of the smallest warheads built
- W61 - the basis for most US weapons today
- W80 - warhead which armed nuclear cruise missiles
- W81 - development of the W61 for the Navy's Standard missile
- W84 - similar development for the Air Force's aborted GLCM missile
- W85 - similar development for the Army's Pershing II missile
- W88 - warhead for the Trident missile