name, this was a whole new missile, and not a development of the Mark I. The Minister of Aviation, Duncan Sandys, insisted that priority be accorded to getting the Mark I into service, and the Mark II was cancelled at the end of 1959. Considerable modification was required to enable the Victors to carry Blue Steel. These included structural changes to the bomb bay. New Conway RCo.17 engines were installed, along with a combuster ignition system to allow all four engines to be started simultaneously and reduce scramble time to minutes per aircraft. A total of 23 Victor B.2 aircraft were upgraded to the new standard, known as B.2R (for retrofit), and two more were built as such. The British government then turned to Skybolt, an American missile that combined the range of Blue Streak with the mobile basing of the Blue Steel, and was small enough that two could be carried on the Vulcan bomber. Armed with a British Red Snow warhead, this would improve the capability of the UK's V bomber force, and extend its useful life into the late 1960s and early 1970s. Cabinet Defence Committee approved the acquisition of Skybolt in February 1960. The Vulcan B.2s were modified to carry a pair of Skybolt missiles. They were fitted with Bristol Olympus 301 engines, strengthened wings and two special attachment points. A British warhead was designed to fit in Skybolt's nose cone, and dummy test firings were carried out at RAF West Freugh commencing on 9 December 1961. It did not prove possible to modify the Victors. The project came to an abrupt halt when the US government cancelled Skybolt on 31 December 1962, but the vestigial attachment points were used for AN/ALQ-101 electronic countermeasure pods during the Falklands War. To replace Skybolt, the Prime Minister, Harold Macmillan, negotiated the Nassau Agreement with the President of the United States John F. Kennedy on 3 January 1963, under which the US agreed to supply the UK with Polaris submarine-launched ballistic missiles instead. This spelt the beginning of the end of the V bombers' nuclear deterrent, but six more years passed before the submarines were built and the Royal Navy was able to take over responsibility. Although originally part of the V force, three squadrons of Valiants were assigned to SACEUR as part of the TBF (Tactical Bomber Force), while remaining part of Bomber Command for training and administration.