The Victor was the last of the V bombers to enter service, with deliveries of B.1s to No. 232 Operational Conversion Unit RAF based at RAF Gaydon, Warwickshire taking place in late 1957. The first operational bomber squadron, 10 Squadron, formed at RAF Cottesmore in April 1958, with a second squadron, 15 Squadron, forming before the end of the year. Four Victors, fitted with Yellow Astor reconnaissance radar, together with passive sensors, were used to equip a secretive unit, the Radar Reconnaissance Flight at RAF Wyton. The Victor bomber force continued to build up, with 57 Squadron forming in March 1959 and 55 Squadron in October 1960. At its height, the Victor was simultaneously operating with six squadrons of RAF Bomber Command.