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BSA M20 file photo [16517]


CountryUnited Kingdom
ManufacturerBirmingham Small Arms Limited
Primary RoleMotorcycle


ww2dbaseWhen World War II commenced, BSA (Birmingham Small Arms Limited) which was Britain's major motorcycle factory, with the proud boast that "one in four is a BSA", responded to a War Office requirement for "a lightweight machine, especially designed for service use" with the submission of a prototype for evaluation developed from their civilian 350cc B30 motorcycle.

ww2dbaseBSA, a company that began as an armaments manufacturer supplying the armed forces, had geared up to produce munitions as early as 1935. Since the late 1920s the company had also presented the War Office with a number of motorcycles for evaluation (and in some cases purchase). In 1936 their model 35-6 had failed to satisfy the Army's requirements because of suspected heavy engine wear, but in the following year a modified version was resubmitted and as a result an order was placed to supply a small batch to the British Army. The War Office then issued a new specification for a lightweight model, specially designed for service use, and BSA, along with the other major manufacturers submitted their own prototype, the M20, for service trials. This was well received and a few had been built when, with war imminent, the official policy changed to favour machines that were already in service. Those companies whose reliability was well known (principally the Norton 16H and BSA M20) received large contracts which eventually led to the M20 becoming the leading service motorcycle employed by the British forces during the Second World War - although it was far from the most popular with its riders.

ww2dbaseThe M20, designed in 1937, as a sidecar model (which overloaded it) utilised a 500cc air-cooled single-cylinder side-valve engine in a heavy frame. Heavy, bulky, slow and with limited ground clearance, the M20 had far from ideal specification, but it was rugged, generally reliable and easily repairable. Special fittings included a long, spiked prop stand for field use and a large headlamp, fitted with a blackout mask in many areas of operation. A shortage of rubber in 1942 led to the replacement of such items as hand grips with canvas fittings and footrests with simple metal ribs. A large air filter mounted on the tank and coupled to the carburettor by a hose was fitted for use in dusty climates such as the African desert, although this necessitated a part of the tank having to be cut away which restricted fuel tank capacity to a mere three gallons.

ww2dbaseSimplicity itself, the M20's rugged engine had massive flywheels, a low compression ratio and soft valve-timing which made it both forgiving and flexible, with plenty of low-down torque. The primary drive chaincase, coupled to a standard BSA gearbox, was a sheet steel pressing secured by a host of small screws, but the exposed rear chain still had to take its chances with desert sand or northern mud.

ww2dbaseFor despatch and escort duty, the M20 became the first choice of the Royal Corps of Signals for despatch riders, serving in many theatres of war. Nearly all were given a liberal coating of khaki paint (often including the engine, tyres and even the saddle) plus suitable camouflage schemes applied in various regions. Despite its considerable weight and strength the M20 was no high-performance machine. Essentially considered to be a "Plodder", the Royal Army Service Corps (RASC) demanded an altogether more responsive machine for convoy and traffic control; preferring the lighter 350cc BSA or 500cc Norton for these roles.

ww2dbaseThe BSA firm produced 126,334 motorcycles for military service between 1939 and 1945 (around 25% of all UK's industrial production) in four models. The bulk of production was either 350cc B30 or 500cc M20 1-cyl models both of which demonstrated great reliability. Vast numbers were sold off at the end of hostilities, and, after gaining a new coat of paint, were eagerly snapped up by a transport-hungry public. The M20 stayed in service in small numbers for many years (in some cases as late as 1971) and many ex-WD M20s can still be found operating in other parts of the world, particularly as new spares are still generally available. A civilian model was manufactured until 1955, and a 600cc cousin the M21, the last side-valve to be built in Great Britain, soldiered on until 1963.

Andrew Kemp and Mirco De Cet, Classic British Bikes (Colour Library Direct, 1997)
Ian V Hogg and John Weeks, The Illustrated Encyclopedia of Military Vehicles (Hamlyn 1980)
John Reed, Motorcycles in WWII (Article in War Monthly, October 1981)

Last Major Revision: Nov 2012


MachineryOne 496cc Single-cylinder air-cooled side-valve four stroke engine rated at 13bhp @ 4200rpm
Length2.18 m
Width0.74 m
Weight0.2 t
Speed90 km/h
Range275 km


British Army dispatch rider on a BSA M20 motorcycle, date unknown

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British Army dispatch rider on a BSA M20 motorcycle, date unknown

Famous WW2 Quote
"I have returned. By the grace of Almighty God, our forces stand again on Philippine soil."

General Douglas MacArthur at Leyte, 17 Oct 1944