Article 3 provided for the sale to the UK of one complete nuclear submarine propulsion plant, as well as the uranium needed to fuel it for ten years. Because of concerns expressed by the JCAE, the AEC would determine the price that Britain would pay for highly enriched uranium (HEU). The treaty did not originally allow for non-nuclear components of nuclear weapons to be given to Britain. It was amended on 7 May 1959 to give Britain access to non-nuclear components and to permit the transfer of special nuclear material such as plutonium, HEU and tritium. The treaty paved the way for the subsequent Polaris Sales Agreement, which was signed on 6 April 1963. The two agreements have been "the cornerstone of the UK-US nuclear relationship for nearly 60 years".