[1] 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.

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.

One advantage of the triplane layout was that each propeller shaft could be symmetrically braced with a pair of X-shaped struts to the upper and lower wings.

There was a radiator on each side of the fuselage near the trailing edge; unusually, these were hinged so that they could be adjusted in flight more or less directly into the slipstream as the pilot chose.

The fin had a straight and vertical leading edge but a curved top that blended into a rounded rudder which extended downwards between separate elevators; the tailplane was mounted just above the fuselage.

After some delay a second Possum was built, flying in April 1925 and transferred to the Aeroplane and Armament Experimental Establishment at RAF Martlesham Heath in August 1925.