The W66 thermonuclear warhead was used on the Sprint anti-ballistic missile system, designed to be a short-range interceptor to shoot down incoming ICBM warheads.
The W66 had a yield of and was an enhanced radiation ("neutron") weapon. The W66 was in diameter and long, with a weight of approximately . The weapon was a two-stage design.
The W66 was based on the Arrow warhead design and by December 1966 had undergone six nuclear tests.