W33 (nuclear warhead)

The W33 was an American nuclear artillery shell, fired from an 8 inch (203 mm) M110 howitzer and M115 howitzer.

A total of 2,000 W33 projectiles were produced, the first of which was manufactured in 1957. The W33 remained in service until 1992. The warhead used 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.

Disinformation or inaccurate reports
Information regarding the W33 has suggested that it was either a double gun and/or that it may have used an annular barrel assembly. The device's internal mechanism was apparently code-named Fleegle. A double gun mechanism reduces the required velocity of each projectile by half, which reduces the gun system weight by a factor of 8. An annular bore may allow a larger projectile which remains subcritical by itself (a hollow projectile has lower effective density, and critical mass scales with the square of density). Titanium was used to reduce weight of some components. Judging by the remaining photographic evidence, it is likely that the exterior casing of the artillery shell itself was made of titanium. This is logical, given that the copper-alloy driving band around the base of the shell is the only part of the shell which engages with the rifling on the artillery piece's barrel.

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.

Tests
The W33 is the third known model of gun-type fission weapons to have been detonated as a test. The W33 was tested twice, first in Operation Plumbbob Laplace, on September 8, 1957 (yield of 1 kt), and the TX-33Y2 in Operation Nougat Aardvark on May 12, 1962, with a yield of 40 kilotons.

Neither test involved firing a W33 from an actual howitzer. Laplace Plumbob was test fired with the device hanging from a balloon at an altitude of 750 feet. Nougat Aardvark was test fired underground, at a depth of 1,424 feet.

Prior gun-type detonations were the Little Boy Mark-1 nuclear weapon used on Hiroshima in World War II, and a test firing of the W9 11-inch nuclear artillery shell in test shot Upshot-Knothole Grable on May 25, 1953.