His Majesty's Naval Base, Clyde (HMNB Clyde; also HMS Neptune), primarily sited at Faslane on the Gare Loch, is one of three operating bases in the United Kingdom for the Royal Navy (the others being HMNB Devonport and HMNB Portsmouth). It is the navy's headquarters in Scotland and is best known as the home of Britain's nuclear weapons, in the form of nuclear submarines armed with Trident missiles. History Faslane was first constructed and used as a base in the Second World War. During the 1960s, the British Government began negotiating the Polaris Sales Agreement with the United States regarding the purchase of a Polaris missile system to fire British-built nuclear weapons from five specially constructed submarines. In the end, only four were constructed; , , and . These four submarines were permanently based at Faslane. Faslane itself was chosen to host these vessels at the height of the Cold War because of its geographic position, which forms a bastion on the relatively secluded but deep and easily navigable Gare Loch and Firth of Clyde on the west coast of Scotland. This position provides for rapid and stealthy access through the North Channel to the submarine patrolling areas in the North Atlantic, through the GIUK gap to the Norwegian Sea. At the time it was chosen, the location was also close to the American SSBN base at Holy Loch, which operated 1961–1992. One boat was always on patrol at any given time. In 1971 the base was home to the 3rd Submarine Squadron of Nuclear Fleet and Diesel Patrol Submarines, "the fighters", and the 10th Submarine Squadron consisting of the four Polaris submarines, "the bombers". In Command Based vessels and units The following notable vessels and units are based at Faslane. Royal Navy Commodore J. L. Perks OBE, Commander Submarine Flotilla/(Commodore Submarine Service (COSM)) Vanguard-class SSBNs Astute-class SSNs HMS Astute HMS Ambush HMS Artful HMS Audacious HMS Anson Sandown-class mine countermeasures vessels HMS Penzance HMS Pembroke HMS Bangor - forward deployed with 9 Mine Countermeasures Squadron in Bahrain Faslane Patrol Boat Squadron (Archer-class patrol vessel) (Archer-class patrol vessel) Northern Diving Group x1 Vahana-class 15m diving support boat Royal Marines (3 Commando Brigade) 43 Commando Fleet Protection Group Headquarters Squadron O Rifle Squadron P Rifle Squadron R Rifle Squadron Island-class patrol vessels Mull Rona Eorsa Serco Marine Services Multicat 2613-class utility boat SD Angeline Coastal oilers SD Oilman SD Waterpress Impulse-class