advice, this formulation was accepted. An American mission now visited the United Kingdom. This was led by Paul H. Nitze, the Assistant Secretary of Defense for International Security Affairs, and included Walt W. Rostow, the Director of Policy Planning at the State Department, and Admiral Ignatius J. Galantin, the head of the SPO. The Americans had ideas about how the programme should be organised. They foresaw the UK Polaris programme having project officers from both countries, with a Joint Steering Task Group that met regularly to provide advice. This was accepted, and would become part of the final agreement. However, a follow-up British mission under Leslie Williams, the Director General Atomic Weapons at the Ministry of Aviation, whose members included Challens and Rear Admiral Frederick Dossor, was given a letter by the SPO with a list of subjects that were off limits. These included penetration aids, which were held to be outside the scope of the Nassau Agreement. One remaining obstacle in the path of the programme was how it would be integrated with the MLF. The British response to the MLF concept "ranged from unenthusiastic to hostile throughout the military establishment and in the two principal political parties". Apart from anything else, it was estimated to cost as much as £100 million over ten years. Nonetheless, the Foreign Office argued that Britain must support the MLF. The Nassau Agreement had invigorated the MLF effort in the United States. Kennedy appointed Livingston T. Merchant to negotiate the MLF with the European governments, which he did in February and March 1963. While reaffirming support for those parts of the Nassau Agreement concerning the MLF, the British were successful in getting them omitted from the Polaris Sales Agreement. The British team completed drafting the agreement in March 1963, and copies were circulated for discussion. The contracts for their construction were announced that month. The Polaris boats would be the largest submarines built in Britain up to that time, and would be built by Vickers Armstrong Shipbuilders in Barrow-in-Furness and Cammell Laird in Birkenhead. For similar reasons to the US Navy, the Royal Navy decided to base the boats at Faslane, on the Gareloch, not far from the US Navy's base on the Holy Loch. The drawback of the site was that it isolated the Polaris boats from the rest of the navy. The Polaris Sales Agreement was signed in Washington, D.C., on