Chevaline

Chevaline (pronounced: Shev-a-leen) was a system to improve the penetrability of the warheads used by the British Polaris nuclear weapons system. Devised as an answer to the improved Soviet anti-ballistic missile defences around Moscow, the system increased the probability that at least one warhead would penetrate Moscow's anti-ballistic missile (ABM) defences, something which the Royal Navy's earlier UGM-27 Polaris re-entry vehicles (RV)s were thought to be unlikely to do.

Chevaline used a variety of penetration aids and decoys to offer so many indistinguishable targets that an opposing ABM system would be overwhelmed attempting to deal with them all, ensuring that enough warheads would get through an ABM defence to be a reasonable deterrent to a first strike. The project was highly secret, and survived in secrecy through four different governments before being revealed in 1980.

The system was in service from 1982 to 1996, when the Polaris A3T missiles it was fitted to were replaced with the Trident D5.

The origins of the Chevaline requirement grew from the conclusion of several British governments that in the event of a Soviet nuclear attack on the UK alone, as had been threatened in late 1950s by Soviet Premier Nikita Khrushchev and Prime Minister Nikolai Bulganin it was unrealistic to expect that the US would retaliate against the Soviet Union and risk an attack on major American cities. That conclusion by successive British governments was the basis of their justification given to the British people for an independent nuclear retaliatory capability.

For some time this deterrent force had been based on the Royal Air Force's V bomber force. This looked increasingly vulnerable in the face of ever-increasing Soviet Air Defence Forces, and by the late 1950s the RAF was pursuing the Blue Steel II standoff missile to allow its bombers to fire their weapons while still (hopefully) outside the range of the defensive fighters.

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