Here are a few things that you may not know.
The Triumph Speed Twin motorcycle engine was designed back in 1937 and continued in production (in various guises) until Bonneville production finally ended in 1988.
But before that the early twin cylinder engine was used in a 6kW auxiliary generating plant, used in Lancaster Bombers.
Between 1960 and 1964 Velocette produced the Viceroy scooter. Powered by a flat twin 2 stoke engine of 250cc.
In later years the Viceroy engine was used in School midget hovercraft projects.