The Avro 608 Hawk was a proposed two-seater fighter variant of the Antelope, which was planned to be powered by a Bristol Jupiter radial engine. Although construction of a prototype began, it was incomplete when it was redesigned with a 540 hp (400 kW) Armstrong Siddeley Panther engine as the Avro 622.
Following interest by Canadian Airways, who had a possible requirement for a mail plane, Roy Chadwick again redesigned the incomplete prototype to the Avro 627 Mailplane . This was a single-engine, single-bay biplane, powered by a 525 hp (391 kW) Panther engine and fitted for wheel or float operation. The sole prototype (G-ABJM) was certificated on 2 August 1931, and was shipped to Canada for operational trials. While these trials were successful, the Canadian government cut the subsidy for civil aviation and so Canadian Airways was unable to afford new aircraft, so the mailplane was returned to England.
The Mailplane was converted in 1933 to a high-speed test bed for the Armstrong Siddeley Tiger engine, the revised aircraft being known as the Avro 654.