The Zuckerman mission found the OPS useful and coming, but there was a big shock. The British were expected to contribute to the research and development costs of the A3, which dates back to 1 January 1963. These were to exceed $700 million by 1968.  Skybolt had been proposed to the United Kingdom at a unit cost, with the United States monitoring the costs of research and development, but no such agreement had been reached in Nassau for Polaris. Thorneycroft was upset by the prospect of paying research and development costs, but McNamara said the U.S. Congress would not represent an agreement that would impose all the burdens on the United States.  Macmillan asked the United Kingdom`s Ambassador to the United States, Sir David Ormsby-Gore, to inform Kennedy that Britain was not prepared to commit to spread the costs of research and development indefinitely, but would pay an additional five per cent for each missile as a compromise. He asked Kennedy to be informed that a failure of the Nassau agreement would likely cause the downfall of his government.  Ormsby-Gore met Kennedy the same day, and while Kennedy noted that the five percent offer was not “the most generous offer he had ever heard of”. McNamara, confident that the United States was scammed, calculated the five percent not only on the missiles, but also on their fire control and navigation systems, adding the bill of about $2 million. On the advice of Ormsby-Gore, this formulation was accepted.
 In January 1979, Callaghan addressed President Jimmy Carter, who reacted positively but without commitment.  The Carter administration`s main priority was the SALT II agreement with the Soviet Union, which limited the stockpile of nuclear weapons. It was signed in June 1979, but Carter faced a fierce fight for its ratification by the United States Senate.  MIRV technology proved to be a major flaw in the 1972 SALT-I agreement, which had a limited number of missiles but no warheads. During the SALT II negotiations, the United States had opposed Soviet proposals to include British and French nuclear forces in the agreement, but the concern was that the supply of MIRV technology to the United Kingdom would be considered by the Soviets as a violation of the spirit of the SALT II non-circumvention clause.  The Polaris Purchase Agreement was a contract between the United States and the United Kingdom that established the British Polaris program. The agreement was signed on April 6, 1963. It has officially ordered the conditions under which the Polaris missile system was made available to the United Kingdom. 7 Nick Ritchie, Trident and British Identity, Department of Peace Studies report (University of Bradford: Bradford, September 2008). Available at www.brad.ac.uk/acad/bdrc/nuclear/trident/briefing3.html Back 9 Mark Bromley and Nicola Butler, Secrecy and Dependence: The UK Trident System in the 21st Century (BASIC: London, November 2001). Available at www.basicint.org/pubs/Research/2001UKtrident1.htm.
Return The terms of the agreement, which was expressed by an exchange of letters between Mrs Thatcher and President Carter, are almost identical to those of the Nassau Agreement of 1962, which preceded the Polaris sale contract. The British team completed the development of the agreement in March 1963 and copies were put into discussion.  Work contracts were announced this month.