The Northrop Gamma started out in 1933 as a private venture involving the latest advances in structural techniques that influenced later generations of aircraft. Later to be designated the A-17, the last military version to bear the name Gamma was the Gamma 5. Only three were built before Northrop switched over production the A-17.
The first Gamma 5 was sold with US government approval to Japan in October 1935. Shipped to Japan the following month, it was evaluated by both Mitsubishi and Nakajima on behalf of the Imperial Japanese Navy and designated the BXN1.
The third Gamma 5 was shipped (again with US government approval) to the Imperial Japanese Navy and designated by the IJN as the BXN2. It was then turned over to Nakajima for further evaluation and is believe to have influenced the design of the Nakajima B5N "Kate" torpedo bomber.
Source: Aerospace Modeler Magazine, No. 7/Summer 2007. "The Northrop Military Gamma Family: Part 1" by Geoff Hays, p36.