<p>A study of the designs initiated by the Vultee Company, especially from the mid-1930s, indicated the introduction of many innovative features. Perhaps one of their most revolutionary design schemes was that for four aircraft to be produced with the same basic tooling and having such assemblies as the wings, aft fuselage and tail unit in common. Variations in powerplant, forward fuselage, landing gear and equipment would ring the necessary changes to provide an advanced, basic or basic combat trainer and a lightweight fighter. While the company probably hoped that such a plan would enable them to get the maximum profit yield from the typical small-scale procurement of the interwar years, it is unlikely that they imagined in their wildest dreams that one aircraft of that quarto would outnumber all other basic trainers produced in the USA during World War II.
</p>
<p>It began in a very small way in 1938 when the US Army Air Corps tested Vultee's BC-3 basic combat trainer, evolved from the BC-51 which was one of the four aircraft mentioned above. The BC-3 had retractable landing gear and a 600-hp (447-kW) Pratt & Whitney Wasp engine and, while testing showed that it had ideal characteristics for a training role, the complexity of a retractable landing gear was unnecessary for the required basic trainer, as was such a powerful engine. As a result, Vultee developed a new Model 74, which had fixed landing gear and a less powerful engine, and US Army testing resulted in an initial contract for 300 aircraft. When placed in September 1939, this was the US Army's largest ever order for basic trainers.
</p>
<p>Designated BT-13 by the USAAC, the new basic trainer was a low-wing cantilever monoplane of all-metal structure, with all control surfaces fabric-covered. Landing gear featured oleo-pneumatic shock-struts, a steerable tailwheel, and hydraulic brakes. Accommodation was provided for a crew of two, seated in tandem beneath a continuous transparent canopy, and dual controls and blind-flying instrumentation were standard.
</p>
<p>BT-13s were soon established in service, and contracts were placed for very large numbers of these aircraft. They were followed on the production line by BT-13As with a different version of the R-985 Wasp Junior engine and detail refinements, and 6,407 of this variant were built. The BT-13B differed only by having a 24-volt electrical system. Production of these airframes was so rapid that the supply of engines dried up, leading to the BT-15 with the 450-hp (336-kW) Wright R-975-11 Whirlwind 9 engine, of which 1,693 were built. The single XBT-16 was a BT-13 constructed by Vidal in 1942 with an all-plastic fuselage.
</p>
<p>The US Navy also had a requirement for basic trainers and, taking the US Army's lead, placed an initial order on 28 August 1940 for a version equivalent to the BT-13A except for the installation of an R-985-AN-1 engine; this had the US Navy designation SNV-1, and 1,350 were built. SNV-2 was the designation of a variant that was the equivalent of the US Army's BT-13B. In all, well over 11,000 of these trainers were built for service with the USAAF and US Navy in the period 1940-44 but, with changing ideas and the introduction of turbine-powered aircraft, all of the aircraft were retired very quickly after the war's end. A handful survived after 1948 to receive the revised designation T-13.
<item><hi format=bold>Powerplant (BT-13A):</hi> one 450-hp (336-kW) Pratt & Whitney R-985-AN-1 Wasp Junior radial piston engine
<item><hi format=bold>Performance:</hi> maximum speed 180 mph (290 km/h); service ceiling 21,650 ft (6,600 m); range 725 miles (1,167 km)
<item><hi format=bold>Weights:</hi> empty 3,375 lb (1,531 kg); maximum take-off 4,496 lb (2,039 kg)
<item><hi format=bold>Dimensions:</hi> span 42 ft 0 in (12.80 m); length 28 ft 10 in (8.79 m); height 11 ft 6 in (3.51 m); wing area 239 sq ft (22.20 m<su>2</su>)
