Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 144,279 pages of information and 230,174 images on early companies, their products and the people who designed and built them.
The BSA M21 was a larger capacity 591cc version of the M20 side valve motorcycle made between 1937 and 1963. Large number were used by the British army. It was also used, with a sidecar attached, as an AA patrol vehicle.