Developed for the 1939 Senior TT, the formidable supercharged V4 was built to respond to the supercharged Italian and German factory racers dominating the TT and Grand Prix circuits at the time.
It was the first machine to lap a Grand Prix course (at Ulster) at over 100mph (161km/h).
The parallel-twin blocks were arranged in a 50 degree V-layout with chain-driven single overhead camshafts.
The supercharger lay across the front of the magnesium crankcases.
One can plainly see the radiator below the steering head in this image.
The round object below that is the supercharger and the large tank behind the gearbox holds oil for the dry-sump lubrication.
The outbreak of World War II prevented racing victory in 1940, and supercharging was banned in 1946 by the Auto Cycle Union (ACU).
This model above is kept on display at the Sammy Miller Motorycle Museum just outside New Milton, Hampshire, England.

It may have been fast, but it was ugly!