Vulcans were selected based upon their engines; only those with the more powerful Bristol Olympus 301 engines were considered suitable. Six aircraft were selected: two each from Nos. 44, 50 and 101 Squadrons. In the event, one was not used. Five crews were chosen, one each from Nos. 44 and 101 Squadrons, two from No. 50 Squadron, and one from the recently disbanded No. 9 Squadron. An air-to-air instructor from the operational conversion unit responsible for training personnel to operate Victor tankers was added to each Vulcan crew during operational missions; this officer was responsible for supervising the refuelling contacts.