Editing UGM-27 Polaris (section)

=== Replacement ===
The British did not ask to extend the Polaris Sales Agreement to cover the Polaris successor [[UGM-73 Poseidon|Poseidon]] due to its cost.{{r|priest2005}} The [[Ministry of Defence (United Kingdom)|Ministry of Defence]] upgraded its nuclear missiles to the longer-ranged [[Trident (missile)|Trident]] after much political wrangling within the Callaghan [[Labour Party (UK)|Labour Party]] government over its cost and whether it was necessary. The outgoing Prime Minister [[James Callaghan]] made his government's papers on Trident available to [[Margaret Thatcher]]'s new incoming [[Conservative Party (UK)|Conservative Party]] government, which took the decision to acquire the [[UGM-96 Trident I|Trident C4]] missile.

A subsequent decision to upgrade the missile purchase to the even larger, longer-ranged Trident D5 missile was possibly taken to ensure that there was missile commonality between the [[U.S. Navy]] and the [[Royal Navy]], which was considerably important when the Royal Navy Trident submarines were also to use the [[Naval Submarine Base Kings Bay]].

Even though the U.S. Navy initially deployed the Trident C4 missile in the original set of its ''Ohio''-class submarines, it was always planned to upgrade all of these submarines to the larger and longer-ranged Trident D5 missile—and that eventually, all of the C4 missiles would be eliminated from the U.S. Navy. This change-over has been completely carried out, and no Trident C4 missiles remain in service.

The Polaris missile remained in Royal Navy service long after it had been completely retired and scrapped by the U.S. Navy in 1980–1981. Consequently, many spare parts and repair facilities for the Polaris that were located in the U.S. ceased to be available (such as at [[Lockheed Martin|Lockheed]], which had moved on first to the Poseidon and then to the Trident missile).