The A.V. Roe Company's design designated as the 504 was typical for its time frame consisting of a wire-braced wooden box girder. Upper longerons were straight in side-elevation. The fuselage was terminated in a vertical sternpost to which was attached a coma-shaped rudder. There was no vertical fin and the tailskid was attached directly to the bottom of the rudder. The 2-bay wings were of equal span. Construction of the 504 design began is April 1913 and the first flight tests were conducted at Brooklands in July 1913.

The aircraft underwent numerous variations, most of which dealt with the type of engine was to be installed. Eventually, the 504K configuration arose. Under this designation adapters were installed by which any of the engine types could be fitted into the 504 airframe. All engines were carried on an overhung mounting and had an open-faced cowling. After a rather undistinguished military career it was realized that the Avro 504K could be used, because of its flying characteristics, was well suited for use as a trainer aircraft. The Avro 504K was such a delight to fly that it laid the foundation for the development in England for logical flying instruction (i.e. the Gosport System). In its mode as a trainer the aircraft was used as the next step, beyond the `Rumpty' in the progression of the student toward flying combat aircraft.

American cadets undergoing flight instruction in England progressed from the `Rumpty' to the Avro 504K before beginning familiarization flights with the aircraft they would be assigned in front-line service.