the role until the Valiants were abruptly withdrawn from service. Work was already under way to replace the Valiants with Victors. A proposal to convert Victor B.1s and B.1As was first considered by the Air Staff on 25 May 1961 and was endorsed by the Chief Scientific Adviser to the Ministry of Defence, Sir Solly Zuckerman, and the Chiefs of Staff in 1963. The Defence Research Policy Committee (DRPC) estimated that converting 27 aircraft would cost £7 million. This would provide sufficient aircraft for three tanker squadrons. The price tag soon increased to £8 million for 24 aircraft, and the Treasury was reluctant to spend that much money pending a review of Britain's overseas defence commitments, which would establish whether a third squadron was required. There were also doubts about the financial viability of Handley Page. Approval was given for the conversion of twelve aircraft on 12 June, three more on 9 July, and another nine on 15 September. The second production Victor B.1 (XA918) was converted into a prototype tanker. This involved the installation of Flight Refuelling Mark 20B pods on each wing to refuel fighter aircraft, two fuel tanks in the bomb bay, and a Flight Refuelling Mark 17 HDU in the bomb bay for bombers and transport aircraft. The grounding of the Valiant tankers injected some urgency into the situation, as the RAF lost its refuelling capability. Six Victor K.1A tankers were delivered to No. 55 Squadron at RAF Marham in May and June 1965, but these were not full conversions, as they had only the underwing refuelling pods, and retained their bombing capability. As Victor tankers became available, a second tanker squadron, No. 57 Squadron, was formed at RAF Marham on 14 February 1966, and a third was added on 1 July 1966 when No. 214 Squadron was re-formed. The last Victor bomber squadrons, Nos 100 and 139 Squadrons, were disbanded on 1 October and 31 December 1968 respectively. It was decided to convert their Victor B.2s into tankers. However, while the Vulcans' rigid delta wing coped well with low-altitude flight, it subjected the Victors' slender wings to considerable flexing, and they suffered badly from fatigue cracks. Repairing them became a major cost of the tanker conversion programme, and some Victors were determined to be beyond economical repair. The Victor SR.2s were withdrawn from service to make up the numbers, and were replaced by Vulcans. Due