The BSA B40 was a series of 350 cc (21 cu in) unit construction single-cylinder OHV four-stroke motorcycles made by the Birmingham Small Arms Company.

[8] The Star had deeply valenced, painted mudguards; metal fork shrouds and the headlamp was fitted in a nacelle.

The machine was fitted with a roller bearing big end and a close ratio gearbox.

[8] Introduced in the US in 1963 as the BSA SS90, the American model was finished in blue and had chrome mudguards and rubber gaiters instead of metal fork shrouds.

[13] First introduced in 1963 in limited quantities[19] the US-only B40 Enduro Star went into full production in 1964.

[20] The model was built around a trials frame a 19" front wheel to give good ground clearance.

It had an alloy tank, single seat, high-level exhaust and a half width 7" front brake.

BSA submitted four B40s built to army specifications for evaluation by the Fighting Vehicles Research and Development Establishment near Chertsey, Surrey.

[27][28] Part of the army specification was that the machine should have a butterfly carburettor as they were concerned that a carb with a slide throttle may stick open in adverse conditions.

Chrome parts were dull-chromed to reduce reflectability and paintwork was "deep bronze green".

[4][29] In total, around 3,000 machines were supplied to the British Military including 141 to the RAF and 34 to the Royal Navy.

[33] The Australian Army stated negotiations for a supply of motorcycles in 1960 with BSA, Triumph, Norton, Velocette and Royal Enfield.

In early 1964 BSA supplied a further 20 of these hybrid machines for an "Extended User Trials" programme.

[30] For 1968, BSA updated the WD inline with the changes to other single cylinder models.

The main customer was Jordan's Arab Army, who ordered 200 machines finished in sand colour.

[32] With poor sales to the military, BSA produced a civilian version, the B40 Roughrider, aimed at Australian sheep farmers.