Northrop used the Gamma transport as the basis of a private-venture design for a light attack bomber, identifying this as the Northrop Gamma 2C which, powered by a 548kW Wright SR-1820F radial engine, was acquired for evaluation by the US Army Air Corps in June 1934 under the designation YA-13. Subsequently re-engined with a 708kW Pratt & Whitney R-1830 Twin Wasp, this aircraft was redesignated XA-16 (Northrop Gamma 2F). Following tests of the YA-13 and XA-16, Northrop received $2 million contract for 110 attack bombers designated A-17, but because testing of the XA-16 had shown that the aircraft was over-powered, the Gamma 2.F was re-engined with a 559kW Pratt & Whitney R-1535 Twin Wasp Junior, serving as the prototype for the A-17. Following the incorporation of several other modifications, the first of 109 production A-17 aircraft was delivered in December 1935. A contract was received in the same month for an improved A-17A, introducing retractable tailwheel landing gear and the 615kW Pratt & Whitney R-1535-13 engine. Some 129 were built, initially by Northrop, but in 1937 Douglas acquired the remaining 49% of Northrop Corporation's stock, and it was the Douglas Company which completed production of these aircraft. Of the total, 93 served with the USAAC for only 18 months, then being returned to Douglas for sale to the UK and France. The Royal Air Force received 60, designating them Nomad Mk I, and all were transferred to the South African Air Force. Douglas also built this aircraft for export under the designation Douglas Model 8A, supplying them to Argentina, Iraq, the Netherlands and Norway. A batch of 34 Model 8A-5 aircraft was also built for Peru, 31 of them being commandeered by the US Army Air Force in early 1942 for use in an attack role. Armed with six 7.62mm machine-guns and able to carry up to 816kg of bombs, all were used in a training role under the designation A-33.