Editing Chevaline (section)

==Further political developments==
The Chevaline project was kept secret by successive UK governments, both Labour and Conservative. This secrecy was maintained under [[Harold Wilson]], [[Edward Heath]], [[Harold Wilson]]'s second term and [[James Callaghan]]. The project was finally revealed by [[Margaret Thatcher]]'s then defence minister [[Francis Pym]].<ref name="nuclear-weapons.info">{{cite web |last1=Burnell |first1=Brian |title=THE ROAD TO TRIDENT: Polaris, PIP, Chevaline - A different view of history |url=http://nuclear-weapons.info/THE%20ROAD%20TO%20TRIDENT%20amended%20draft%202019.pdf |access-date=31 May 2022}}</ref>

The reasons for revelation were both political and practical. The cost over-runs of the project were now so enormous (approximately £1 billion by 1979) that the secret inner-Cabinet spending approvals could not continue. The key decision to proceed had been taken in 1975, four years previously, and cancellation would be unlikely to save money at that point. Even if it were to be cancelled, a replacement would have to be ordered in any case. Shortly afterwards the [[First Thatcher ministry|Thatcher government]] decided that the successor system should be the [[Trident missile|Trident]] system and ordered the [[UGM-96 Trident I|C4 variant]].

The Naval Staff angst that had been a feature of the Chevaline project surfaced here too. For several reasons the Navy had not wanted Chevaline and had actively lobbied against it. Their preference for Poseidon was in large part based on commonality of equipment. Polaris was being phased out of use by the US Navy and supplies of spares and repair facilities were becoming unavailable. To keep the Polaris missile in use in the UK meant that some production lines had to be re-opened at great cost to supply a very small force. A missile common to both navies was desirable, and the Naval Staff strongly argued against Chevaline. At one point, several of their counterparts in the US Navy had encouraged them to seek congressional approval for such a proposal through a formal request from the Ministry of Defence.<ref>{{cite journal |last1=Stoddart |first1=Kristan |date=10 September 2010 |title=The British Labour Government and the development of Chevaline, 1974–79 |url=https://www.tandfonline.com/doi/abs/10.1080/14682741003679375 |journal=[[Cold War History (journal)|Cold War History]] |volume=10 |issue=3 |pages=287–314 |doi=10.1080/14682741003679375 |s2cid=155022081 |access-date=23 February 2023|url-access=subscription }}</ref> Although the papers will not be declassified for some time yet, it seems likely that the Naval Staff made the same case with Trident with some success when their influence was at its height after the [[Falklands War]].

The US later decided to move primary development from the C4 to the larger Trident D5, a much more capable missile, but one that would not fit into the latest {{Sclass|Ohio|submarine|1}}s, let alone the older {{Sclass|Benjamin Franklin|submarine|4}}. Their solution to this problem was to change the design of the ''Ohio'' class to allow for the larger D5. Thatcher, who was fully committed to Trident, decided to follow the same route and authorized the design of the {{Sclass|Vanguard|submarine|0}} to carry them. They agreed to a deal whereby the US and British combined missile stock is serviced at a single location at the US Navy facility at Kings Bay, [[Georgia (U.S. state)|Georgia]], and from there missiles are issued to both US and British submarines. Only the warheads (added later to British missiles) are different.

Finally, recently published recollections from senior members of the development team are explicit in stating that Chevaline was not the best, or with hindsight, the cheapest choice the British could have made from the many options available. But the choices were never simple but overlaid with what was politically possible, what was in the best interests of UK industry and its scientific base. In the end, the alternatives were ''"between Chevaline or nothing at all; a decision which could easily have meant withdrawal of the UK from the military political nuclear scene"'' and that option was unthinkable to the military staffs and government alike.<ref name="nuclear-weapons.info"/>