The Boulton Paul Balliol and Sea Balliol are monoplane advanced trainer aircraft designed and produced by the British aircraft manufacturer Boulton Paul Aircraft. On 17 May 1948, it became the world's first single-engined turboprop aircraft to fly. The Balliol was operated primarily by both the Royal Air Force (RAF) and the Royal Navy Fleet Air Arm (FAA). Developed during the late 1940s, the Balliol was designed to fulfil Air Ministry Specification T.7/45, replacing the wartime North American Harvard trainer. Unlike previous trainer aircraft, which were powered by piston engines, it was specified for the aircraft to use newly developed turboprop propulsion instead. On 30 May 1947, the Balliol performed its maiden flight; the first preproduction aircraft would fly during the following year. Production examples were powered by the Rolls-Royce Merlin engine, while various prototypes and pre-production aircraft featured alternative powerplants such as the Rolls-Royce Dart and Armstrong Siddeley Mamba turboprop engines. The Balliol entered service with the RAF during 1950 and proved to be a relatively trouble-free trainer. However, a shift in attitudes towards turbojet-powered trainer aircraft would see orders being curtailed for the type by 1952. Despite this, a navalised version of the aircraft, the Sea Balliol, was also introduced for deck landing training. The type also saw some use in other capacities, such as for experimental flights. Only a single export customer, the Royal Ceylon Air Force, would procure the type. Development Origins During March 1945, the Air Ministry issued Specification T.7/45, which sought a new advanced trainer to succeed the Royal Air Force's (RAF) fleet of North American Harvard. Amongst the requirements specified was the use of the newly developed turboprop engine, as it was felt that the new generation of advanced trainers would better prepare pilots for flying jet-powered combat aircraft such as the newly emerged Gloster Meteor fighter aircraft. As a fallback measure in case of difficulties being encountered with engine development programmes, the envisioned trainer was also to readily accommodate a more conventional Bristol Perseus radial engine as well. A further stipulation by the ministry was the fitting of a three-seat cockpit in a configuration roughly akin to the contemporary Percival Prentice basic trainer. The pilot and instructor were sat in a side-by-side arrangement, while a second student could be accommodated in a third seat to the rear, positioned as to enable them to closely observe the pilot and the instructions being issued. The