In early 1921 design was initiated of the Vickers Vulcan transport, a 49 ft 0 in (14.94 m) span biplane with a deep oval-section fuselage completely filling the space between the equal-span wings. It accommodated the pilot in an open cockpit forward of the upper wing, with below and behind him a roomy enclosed cabin for six to eight passengers. To limit selling price to the minimum the low-cost war-surplus 360 hp (268 kW) Rolls-Royce Eagle VIII engine was installed in the first six aircraft (Type 61) to be completed, but as a number of performance problems were encountered the last two examples (Type 74) had the 450 hp (336 kW) Napier Lion. One of the early production aircraft was completed as a cargo carrier (Type 63) for Air Ministry evaluation, but was subsequently reconverted as a passenger carrier and used with one other Eagle-powered and the two Lion-powered aircraft by Imperial Airways on European service. However, their very limited reliability meant the Vulcan had only a short useful life, only one or two surviving in service beyond the mid-1920s.