<p>The long, lean years which stretched from the end of World War I until the late 1930s had, so far as the US Army Air Corps was concerned, done little to expand the force which had been pruned back almost to the roots in the aftermath of the Armistice and the Treaty of Versailles. The outbreak of war in Europe in 1939 brought the realization that something must be done immediately to train large numbers of pilots to fly airplanes that did not then exist, leading to the procurement of training aircraft on an unprecedented scale.
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<p>Competing in one of the many prototype competitions for primary trainers in 1939-40 were the St Louis Model PT-1W and the Waco Model UPF-7, both biplane primary trainers which had been built for the civil aircraft market. They were of particular interest to the USAAC because the procurement of an aircraft which was already in production would fill the training gap far more quickly than would the issue of a contract for the design and development of an entirely new trainer, even if it meant accepting something marginally below the desirable standard.
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<p>Testing of an example of the St Louis trainer, given the designation XPT-15, resulted in a follow-up order for a small batch of 13 YPT-15 pre-production aircraft. These were single-bay stagger-wing biplanes of clean appearance, with a minimum of struts and bracing wires, and provided with ailerons on the lower wing only. The basic structure was all-metal, with fabric covering on all the aerofoil surfaces and a metal skin on the fuselage. Landing gear was of the nonretractable tailwheel type, the cantilever main units being well faired to reduce drag. Powerplant consisted of a Wright R-760-1 Whirlwind 7 engine, uncowled but faired so that only the cylinder heads and a forward-mounted exhaust ring were exposed. Instructor and pupil were accommodated in tandem open cockpits, and dual controls and full instrumentation were standard.
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<p>All of the trainers were delivered in 1940, and although used in the primary training role they were regarded only as stop-gaps until aircraft procured to US Army specification became available, and no additional orders ensued.
<item><hi format=bold>Performance:</hi> maximum speed 130 mph (209 km/h); cruising speed 116 mph (187 km/h); service ceiling 15,000 ft (4,570 m); range 350 miles (563 km)
<item><hi format=bold>Weights:</hi> empty 2,059 lb (934 kg); maximum take-off 2,766 lb (1,255 kg)
<item><hi format=bold>Dimensions:</hi> span 33 ft 10 in (10.31 m); length 26 ft 5 in (8.05 m); height 9 ft 5 in (2.87 m); wing area 279.9 sq ft (26.00 m<su>2</su>)
