<hi style=afpcap>Although famed for generations as a builder of airliners and cargo aircraft, Douglas experimented with the early bomber design. Two near identical prototypes were produced in 1931 designated the XO-35 and XO-36 (later the XB-7) , with orders for service test aircraft being placed in 1932. The bombers featured innovations as their were constructed with all-metal fuselage and wings, and featured retractable undercarriages.</hi>