It was decided to opt for a large first batch, totalling 136 aircraft, as this allowed for the implementation of more economical flow-line production at Airspeed's Portsmouth factory. On 19 June 1937, the first prototype Oxford, "L4534", conducted its first flight at Portsmouth. Initially, two variants were planned; the Mark I, which was viewed as a general-purpose training aircraft equipped with a dorsal gun turret, and the Mark II, which lacked any turret but was instead fitted with dual controls. As further large contracts for the aircraft were placed with Airspeed, (100 Mk Is and 100 Mk IIs) it was arranged that de Havilland Aircraft would build them at Hatfield later, to meet the demands for Oxfords for training. Other companies also manufactured the aircraft.