<p>Although this designation is today unfamiliar, the airplane to which it applied is one of the best-known shapes in the sky. In 1935, General Aviation (soon to be renamed North American) had flown the NA-16 trainer prototype, from which had been developed the BT-9 basic trainer. In 1937, the Army Air Corps ran a competition for a basic combat trainer, and North American returned to the NA-16 prototype for inspiration. A big Wasp engine was fitted, driving a variable-pitch propeller and a hydraulic system, the latter allowing a retractable undercarriage to be fitted. This retracted inwards into uncovered wells under the leading edge and center-section, necessitating the fitment of characteristic circular fairings at the wingroot. Provision was made for light armament for weapons training, and radio. Under the company designation NA-26, the new prototype easily won the competition, and was rewarded with an order for 41 aircraft under the military designation BC-1 (NA-36). An additional 139 were built for the Air Corps, of which 30 were modified to act as instrument trainers under the designation BC-1I. The final three aircraft were built with wings and rudder redesigned to facilitate production, and with the Pratt & Whitney R-1340-45 engine driving a three-bladed propeller. These were known as BC-2s (NA-54).
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<p>The major production version was the BC-1A (NA-55), which had revised wings and was the first of the series to introduce a straight trailing edge to the rudder. Ninety-two were ordered, of which one became the BC-1B with a redesigned center-section, and nine were delivered with a new designation that would be far more famous than the original: AT-6. Although it had a different company number (NA-59), the initial batch of AT-6s was no different to the preceding BC-1As, reflecting only the 1940 decision to drop the Basic Combat (trainer) category and revive the dormant Advanced Trainer category. Of course the AT-6 became the best-known trainer of the war, and served in this role into the 1990s. AT-6 variants are described under that heading.
