W33 (nuclear warhead)

American nuclear artillery shell

The W33 (also known as the Mark 33, T317 and M422) was an American nuclear artillery shell designed for use in the M110 howitzer and M115 howitzer. A total of 2,000 W33 projectiles were produced, with the first production warheads entering the stockpile in 1957. The W33 remained in service until 1992. The warhead used enriched uranium (code named oralloy) as its nuclear fissile material and could be used in two different yield configurations. This required the assembly and insertion of different pits, with the amount of fissile materials used controlling whether the destructive yield was low or high. The highest yield version of the W33 may have been a boosted fission weapon.

Development of the W33 was authorized by the Army Ordnance Corps in June 1953. It was believed that a shell capable of being fired by a standard mobile field howitzer would be more effective while also providing a psychological effect in ground warfare. The design would also include consideration for being fired from navy guns, and would use nuclear components from the W9 nuclear artillery shell. The initial army designation for the weapon was Shell, AE, 8 inch, T317 and the Atomic Energy Commission (AEC) nomenclature was Mark 33. The army were assigned the task of designing, constructing and stockpiling the non nuclear components of the weapon, while the AEC were assigned the design and construction of the nuclear components. The W33 mechanism has been reported to have comprised two critical nuclear parts which were required to assemble a complete W33 warhead. The initial disassembly of stockpiled W33 warheads in 1992 proceeded first by disassembling all existing parts for one of the components, and then disassembling the other one in following years. The weapon had four yield variants, known as the Y1 through Y4, and written using the standard nomenclature in the form of W33Y1 etc. The yield of each type remains classified, but it has been alleged that the Y2 version had a yield of and the other versions were .

The W33 is the third known model of gun type fission weapons to have been detonated, and the second as a test explosion. The W33 was tested twice, first in Operation Plumbbob Laplace, on September 8, 1957 with a yield of , and the TX 33Y2 in Operation Nougat Aardvark on May 12, 1962, with a yield of
Neither test involved firing a W33 from an actual howitzer. Plumbbob Laplace was test fired with the device hanging from a balloon at an altitude of 750 feet (229 m). Nougat Aardvark was test fired underground at a depth of 1424 feet (434 m). Prior gun type detonations were the Little Boy Mark 2 nuclear weapon used on Hiroshima in World War II, and a test firing of the W9 nuclear artillery shell in test shot Upshot Knothole Grable on May 25, 1953.