To enter the fast growing domestic military market, Ryan developed an airplane for evaluation in the 1939 U.S. Army Air Corps primary trainer competition. The Army tested it as the XPT-16. Its performance won a 15-plane service evaluation order, these to be designated YPT-16s. The Ryan ST as had been built in strict accordance with military requirements. In the redesign for the YPT-16s, the basic and familiar ST airframe underwent its first external appearance change. The cockpit openings were cut larger, down to meet the channel stiffeners, addition of a turnover mast at the front cockpit windshield, a Bendix hand-cranked direct drive inertia engine starter, toe brakes and parking brake completed the redesign. This met the immediate military specifications and was the first low-wing trainer to convince the Army to break away from their 30-year precedent of biplanes being used for initial instruction of aviation cadets.