One of the first projects for the former Stearman Aircraft Company which in 1939 had become the Wichita Division of Boeing was a twin-engined trainer for bomber crews.

Designated X-120 by the company, two examples were ordered by the United States Army Air Corps as the XAT-15.

It had a retractable tailwheel landing gear and an extended glazed fuselage nose for the trainee bomb-aimer.

Due to shortage of materials, the aircraft was built of welded steel tube covered with plywood, with wooden wings and tail unit.

According to Edward H. Phillips, "The aircraft's specific purpose would be to teach prospective bomber crews how to work together as a team before they were assigned to an operational unit."