The US and French facilities Alex Salmond refers to as a potential base for the UK’s four Vanguard-class nuclear missile submarines are the Naval Submarine Base Kings Bay in the state of Georgia and L’Ile Longue Submarine Base, near Brest.
These specialist facilities have the “deep water” channels that military planners find favourable for the stealthy departure and return of the submarines, as well as the expensive and complex support infrastructure needed to keep the vessels serviceable and their crews trained.
The French base currently hosts four of the vessels, termed “SSBNs” for submarine ballistic nuclear missiles, from the Triomphant class. Each French submarine carries 16 vertically launched M45 or M51 ballistic missiles manufactured by EADS Space Transportation. The French nuclear deterrent can be regarded as more truly independent than the UK’s, as its missiles and warheads are both domestic products, in contrast to the UK, which has considerable US involvement with even the non-nuclear part of the Trident warheads.
In the US, Kings Bay itself was only constructed as a specialist SSBN base in the late 1970s, after a new United States naval-basing agreement with Spain included the withdrawal of its fleet ballistic-missile submarine squadron from the base at Rota, in Spain.
The Trident Training Facility (TTF) at the base provides technical training to sailors in the operation and maintenance of Trident ballistic-missile submarines and guided-missile submarines and systems.
The UK currently leases its Trident II D-5 missiles from the US, but they are actually held with the Atlantic squadron of the US Navy’s Ohio-class SSBNs at Kings Bay. The store is “co-mingled” and missiles are selected at random for loading onto either country’s submarines.