Source:
Tony Buttler; "The Next Chapter", Aeroplane, June 2020, pp.42-47.
This includes around 1 1/2 pages of text, with original layout and detail drawings of the three types discussed below.
The Type 327 was preceded by the Types 324 and 325, in response to Specification F18/37 issued in March 1938, aimed at a Spitfire and Hurricane replacement and demanding more Brownings than you could shake a stick at. Supermarine offered the Type 324 in two options, with twin Merlins or twin Bristol Taurus radials. Alongside that it offered the same engine combis but with pusher props. All would have had the two engines rotating in opposite senses to cancel out torque. Speeds were predicted to be 10 mph more than the equivalently-engined Spitfire.
Sizes varied slightly, spans being just over 40 ft and lengths over 31 ft. The main u/c was attached behind the engines and retracted inwards into the rather thick wing. All had nosewheels.
Supermarine lost out to Hawker's two variants, which resulted in the R-R Vulture powered Tornado prototype and the ultimately successful Napier Sabre driven Typhoon. But Supermarine did not give up, picking up on the trend towards cannon with a six-cannon variant, the Type 327, and positioning it as a fallback for the Westland Whirlwind already under development. They were awarded a contract for a full-scale mock-up, but that was as far as it ever got. The Bristol Beaufighter would presently fill the gap left by the struggling Whirlwind.