W68

The W68 warhead was the warhead used on the UGM-73 Poseidon SLBM missile. It was developed in the late 1960s at Lawrence Livermore National Laboratory.

Specifications
The W68 weighs 367 lb. The warhead's dimensions are not publicly known, however to fit the maximum load of 14 within the roughly 65 in Poseidon payload fairing, the Mk 3 Reentry Vehicle must be much smaller than other US RVs [which are mostly 22 in diameter and mostly 72 in long sized].

The W68 had a design yield of 40-50 kilotons.

Production and deployment
A total of 5,250 W68 warheads were produced, the single largest production run of any American nuclear weapon model. It was manufactured starting in June 1970 and ending in June 1975. Each Poseidon missile could carry up to 14 warheads; at the peak deployment, there were 41 US Poseidon submarines with 16 missiles each, for a total of 656 deployed missiles, at a density of about 10 warheads per missile.

Safety issues and later service
Aging of the LX-09 Plastic Bonded Explosive used in the W68 led to decomposition of the explosive, separating the binder and plasticizer, which then caused deterioration of the detonators. This required the whole production run to be retired or remanufactured with LX-10 and LX-10-1 as new explosives from November 1978 through 1983; about 2,000 units were retired starting in 1977 rather than rebuilt.

The remaining 3,200 warheads remained in service longer, with the last units retired in 1991.