Developed in the early 1950s, the Napier Eland turbo prop engine was first bench tested in 1952. The first air tests were carried out in 1953 with a modified Vickers-Armstrong Varsity aircraft. Within its first ten hours of flight test, the Eland had been operated at an altitude of 30,000 feet and successfully restarted at 25,000 feet. These milestones are thought to be a first for a turbo prop engine. Seeing a market for the Eland, in re-engining current piston aircraft, Napier purchased a Convair CV-340. Napier replaced the CV-340’s two R-2800 piston engines with Elands. The changeover was straight forward and no modification were made to the engine firewall or to the airframe.
The Royal Canadian Air Force placed an order for ten Eland-powered Convairs in March 1958. These airframes were to be built by Canadair in Montreal, as the CL-66. The first CL-66B for the RCAF flew on January 7, 1960 and the all ten were delivered by March 1961. The CL-66 was redesignated the CC-109 Cosmopolitan in RCAF service. Suffering from reliability problems and a short life between engine rebuilds the RCAF decided to re-engine the Cosmopolitan with the more reliable Allison T-56 turbo prop engine. In 1961 Rolls Royce acquired the assets of Napier’s engine division and the Eland was dropped from production. The Convair 540 and CL-66 were the only production aircraft to be fitted with the less than successful Eland engine.