The vast majority of BSA M20 models delivered were employed by the War Department (Army), although smaller quantities were also used by both the Admiralty (Navy) and the Air Ministry (RAF). The RAF was issued with quantities of Swallow sidecar combinations, and many of of the smaller M20 model contracts throughout the Second World War specified sidecar-lugs for the frame, generally removed from all the larger contracts, which were specifically solo only.
Although intended as a general-purpose motorcycle for convoy escort and long-distance communications duties, due to the sheer number supplied the model was employed ultimately in every theatre of war and for every imaginable purpose, whether suitable or not. It is perhaps for this reason that the model is the one best remembered by and familiar to most ex-servicemen.
Desert colours: khaki brown was used on most North African theatre machines