 An order for three prototypes was placed in October 1921, together with three of the competing design from Blackburn Aircraft, the Blackburn Blackburn.Avro's design, the Type 555 Bison, was a two-bay biplane, powered, like the Blackburn, by a Napier Lion engine.The deep slab-sided fuselage was constructed of steel tube, with the pilot sitting in an open cockpit forward of the wings, and the engine cowling sloping steeply down ahead of the pilot.