The Parnall Possum was one of few large aircraft having its engine in its fuselage and the propellers on its wings. The concept arose immediately after World War I, when the British & Colonial Aeroplane Co. (later Bristol), began thinking about large transport aircraft powered by steam turbines mounted in an "engine room" in the fuselage and driving wing-mounted propellers. They intended to develop the idea using their large Bristol Braemar triplane bomber, initially modified to be powered by four 230 hp (172 kW) Siddeley Pumas and called, in anticipation of steam power the Tramp. They obtained Air Ministry support for this project, the Ministry appreciating the extra safety of an aircraft whose engines could be serviced in flight. The Ministry also issued specification 9/20 for a smaller aircraft of the same configuration and placed orders for two prototypes with Parnall, for the single-engined Possum and with Boulton & Paul for the twin-engined Bodmin. They were described as "Postal" aircraft but were clearly experimental bombers; all three types were built but only the Possum and the Bodmin flew.
