increased the range by . The second production B.2, XH558, was delivered to No. 230 Operational Conversion Unit on 1 July 1960. As Vulcan B.2s were received, the B.1s were withdrawn from service and upgraded to B.1A standard through the installation of more electronics. Most of this work was carried out by Armstrong Whitworth. Modifications were made to the Victor B.1 in 1959. These included the addition of an in-flight refuelling probe, new electronic countermeasures (ECM) equipment, tail-warning radar, drooped leading edges and a strengthened pressure cabin. This modified version was known as the Victor B.1A. An improved version of the Victor was also programmed with the Armstrong Siddeley Sapphire 9 engine, an improved version of the Sapphire 7 in the Victor B.1. However, development of the Sapphire 9 was cancelled by the Ministry of Supply in February 1956, and a minor improvement to the Sapphire 7 in March 1956 increased its thrust to , so it was decided to ship 25 of the next production batch of 33 Victors ordered in May 1955 with the Sapphire 7. The remaining eight, along with 18 more Victors ordered in January 1956, were built as Victor B.2s, with the Rolls-Royce Conway RCo.11 engines providing . The new Conway engines required redesigned enlarged intakes to provide the greater airflow required, and the wingspan was extended from . As in the Vulcan, the DC electrical system was replaced with an AC one. The prototype Victor B.2, XH668, first flew on 20 February 1959, but was lost over the Irish Sea on 20 August. The first production B.2, XL188, was delivered on 2 November 1961, and No. 139 Squadron became the first Victor B.2 squadron on 1 February 1962. V force assets at the end of 1962 were: The V Bomber force reached its peak in June 1964, when 50 Valiants, 70 Vulcans and 39 Victors were in service. In retrospect, the decision to proceed with three V bombers was questionable. As it turned out, all the roles could have been performed by the Valiant, and its B.2 model was specifically designed for the low-level operations that the V bombers would employ in their later years. Moreover, the rationale for producing both the Vulcan and the Victor disappeared early on. That for producing the Victor B.2 instead of concentrating on the Vulcan B.2 was especially dubious, and Air Chief Marshal Sir Harry Broadhurst attributed it