Editing Chevaline (section)

==Military and political requirements==

The origins of the Chevaline requirement grew from the conclusion of several British governments that in the event of a [[Soviet Union|Soviet]] nuclear attack on the UK alone, as had been threatened in late 1950s by Soviet Premier [[Nikita Khrushchev]] and Prime Minister [[Nikolai Bulganin]]<ref>A.J.R.Groom, "British Thinking About Nuclear Weapons", Frances Pinter, 1974, pp. 190–191. {{ISBN|0-903804-01-8}}</ref> it was unrealistic to expect that the US [[second strike|would retaliate]] against the Soviet Union and risk an [[countervalue|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 various reports by the RAF suggested their bombers would be incapable of successfully delivering free-fall ("gravity") bombs by 1960. This had been considered from the early 1950s and the planned solution was a move to the [[Blue Streak missile|Blue Streak]] [[medium range ballistic missile]], but this suffered extensive delays for a variety of reasons.

As it became clear Blue Streak would not be available by 1960, interim solutions were considered. Among many possibilities, the RAF eventually selected the [[Blue Steel missile|Blue Steel]] [[standoff missile]] to allow its bombers to fire their weapons while still (hopefully) outside the range of [[Soviet Air Defence Forces|the defensive fighters]]. This system provided marginal capability and a number of projected developments were considered as Blue Steel II, which increased both its range to improve the survivability of the bomber and speed to improve the survivability of the missile.

A better solution came along in the form of the US's [[AGM-48 Skybolt]] missile. The US bomber force was facing the same sorts of problems as the British V bombers, and were attempting to solve it in a similar fashion, with a long-range standoff missile. In this case the missile had a projected range of just under {{convert|2000|km}}. The distance from London to Moscow is about {{convert|2500|km}}, so Skybolt would allow the V-bomber force to attack Russia from sites not far off the British coast, with complete impunity.  Skybolt seemed like such a good solution that work on both Blue Steel II and Blue Streak were cancelled.

Skybolt development was cancelled in early 1962 and led to a major political row. Finally a compromise was reached later that year; the [[Nassau Agreement]] had the [[Royal Navy]] taking over the deterrent role with newly acquired [[Polaris missile]]s. This arrangement was formally outlined in the [[Polaris Sales Agreement]].

One key part of the agreement was that the UK would develop their own [[warhead]]s for the missiles, as the UK military and political establishments were rather worried about losing their own nuclear production and design capability. Having already put some effort into the Skybolt warhead, it was decided to adapt this design, based on the thermonuclear secondary of the US [[W59]], matched to a primary trigger based on a wholly UK design developed from the Cleo device tested at the Pampas instead of the [[W58]] used on US Navy missiles.