The Polaris Sales Agreement was signed on 6 April 1963. The UK retained its deterrent force, although its control passed from the RAF to the Royal Navy. The Polaris missiles were equipped with British warheads. A base was developed for the Polaris submarines at Faslane on the Firth of Clyde, not far from the US Navy's base at Holy Loch. It was served by a weapons store at nearby Coulport. The first of four Polaris submarines, was launched in September 1966, and commenced its first deterrent patrol in June 1968. The annual running costs of the Polaris boats came to around two per cent of the defence budget, and they came to be seen as a credible deterrent that enhanced Britain's international status. British politicians did not like to talk about "dependence" on the United States, preferring to describe the Special Relationship as one of "interdependence".