The Morane-Saulnier BB was a military observation aircraft produced in France during World War I for use by Britain's Royal Flying Corps. It was a conventional single-baybiplane design with seating for the pilot and observer in tandem, open cockpits. The original order called for 150 aircraft powered by 110-hp Le Rhône 9J rotary engines, but shortages meant that most of the 94 aircraft eventually built were delivered with 80 hp Le Rhône 9C rotaries instead. A water-cooled Hispano-Suiza engine was trialled as an alternative in the Type BH, but this remained experimental only.
The type equipped a number of RFC and RNAS squadrons both in its original observation role and, equipped with a forward-firing Lewis gun mounted on the top wing, as a fighter.