Designed to a 1935 specification, the Beaufort was initially referred to as the "Super-Blenheim".
A prototype was ordered by the Air Ministry in 1937 with Bristol Perseus engines, quickly changed to Bristol Taurus types & first flying on 15 Oct, 1938. It entered RAF service in November 1939 but by May 1940 the trouble-some Taurus engines led aircrews to threaten mutiny. The search for better engines initially settled on the Rolls-Royce Merlin & (without permission) Bristol made several dozen sets of engine-frames to mount these in the Beaufort making it the Beaufort MkII.
As the Merlin was needed for Spitfires, Lancasters etc, the decision to use the Pratt&Whitney R-1800 radial as already used in the Australian-built DAP Beaufort Mk.VII was made. The British installation was slightly different to the Aussie version (air intakes etc).
The RAF designated the P&W engined Beaufort the MK.II. so Bristol re-designated their Merlin Beaufort the MK.III. Bristol's unauthorised Merlin mounts were then used in the Beaufighter II.
