The mid-1950s development of the submarine-launched Polaris ballistic missile by Lockheed and the US Navy led to the eventual signing of a Polaris Sales Agreement between Prime Minister Harold Macmillan and President John F Kennedy.
It was decided than the United Kingdom would have four Polaris submarines to carry the latest A-3 missiles; that the submarines would be British designed and built; that the whole weapon systems and equipment, except warheads, would be purchased from the United States; and that the warheads would be British. The Government directive was explicit; the four SSBNs (Ship Submersible Ballistic Nuclear) were to be deployed at the earliest possible date and the programme
