The treaty provided for the sale to the UK of one complete nuclear submarine propulsion plant, as well as ten years' supply of enriched uranium to fuel it. Other nuclear material was also acquired from the US under the treaty. Some 5.4 tonnes of UK-produced plutonium was sent to the US in return for of tritium and 7.5 tonnes of highly enriched uranium (HEU) between 1960 and 1979, but much of the HEU was used not for weapons but as fuel for the growing fleet of British nuclear submarines. The treaty paved the way for the Polaris Sales Agreement, and the Royal Navy ultimately acquired entire weapons systems, with the UK Polaris programme and Trident nuclear programme using American missiles with British nuclear warheads.