BSA's 400cc model M20 was introduced in 1938. With World War II imminent, the British government quickly ordered 8,000 M20's for military use. Heavy and cumbersome with low ground clearance, it wasn't the ideal battlefield machine, but above all it was supremely reliable and easy to build. Over 126,000 were built for the Allied forces and remained as the primary military motorcycle for 20 years. Sometimes the handgrips were made out of canvas when rubber was in very short supply.
One was used in raiders of the lost ark by a villain