 They were to be used for evaluation by the Royal Air Force and Royal Navy which has both issued specifications in 1953 for tandem helicopters.The Royal Navy requirement (Specification HR.146) was for a Leonides Major-powered aircraft for a shipborne helicopter for anti-submarine, rescue and transport duties, Specification HR.149 was for a similar aircraft for the Royal Canadian Navy.The Royal Air Force issued specification H.150 for a general-purpose transport helicopter with the ability to lift bulky external loads.