W81
The W-81 thermonuclear warhead was a planned US warhead to be mounted on the SM-2 surface to air missile used by the US Navy. The W-81 was a design derivative of the B61 nuclear bomb as many other modern US warhead designs are. The weapon was being designed at Los Alamos National Laboratory (at the time called Los Alamos Scientific Laboratory).
The W-81 went through several design iterations, starting with an enhanced radiation model, then a pure fission model, and finally was simply cancelled in 1986 without ever being tested or produced.
Characteristics are not known in detail, but the B-61 it is derived from has a physics package (bomb core) of about 12 inch diameter with length of 32 inches, weighing around 300 pounds (see the W80, another B-61 derived design). Available LASL images show a much shorter weapon, perhaps 12 by 16 to 18 inches, probably the final fission-only W-81 concept, corresponding with the size of the B-61 fission primary alone.
