abstract:Chevaline (pronounced: Shev-a-leen) was a project to improve the penetrability of the warheads used by the British Polaris nuclear weapons system. Devised as an answer to the improved Soviet defences around Moscow, the system was intended to increase the probability that at least one warhead would penetrate the city's anti-ballistic missile (ABM) defences, something which the Royal Navy's earlier Polaris re-entry vehicles (RV)s were thought to be unlikely to do.