Originally with open tandem cockpits, the NA-16 was of metal construction with a fabric-covered fuselage, and was provided with fixed tailwheel type landing gear. Powered by an non-cowled 400 hp (298 kW) Wright R-975 Whirlwind engine, the prototype was first flown on 1 April 1935 in Dundalk, Maryland by test pilot Eddie Allen. After evaluation at Wright Field, was selected for production for training under the designation BT-9, albeit with some modifications which were to include enclosed cockpits.

Although the prototype, as the NA-18, was so modified and fitted with a 550 hp (410 kW ) Pratt & Whitney R-1340-41 Wasp air-cooled 9-cylinder radial engine, the 400 hp (298 kW) Wright R-975 Whirlwind 9-cylinder radial engine was retained for the production BT-9. The first of 42 BT-9s produced was flown at Inglewood, Los Angeles (North American's new factory) in April 1936. Forty BT-9As, with one fixed forward-firing gun, and another on a flexible mounting in the rear cockpit, were then built for the USAAC Reserve, followed by 117 BT-9Bs with detail improvements, and the series ended with 67 similarly armed BT-9Cs with only equipment changes. The first of the BT-9Cs was, in fact, completed as the sole Y1BT-10, with a 550 hp (410 kW) Pratt & Whitney R-1340-41 radial engine, and another single aircraft was designated BT-9D to signify a change, namely the substitution of the more angular outer wing panels and rudder which had, by then, been developed for the BC-1A.

The US Navy received 40 aircraft designated NJ-1, which were basically BT-9s with the 550 hp (410 kW) Pratt & Whitney R-1340-41 Wasp 9-cylinder engine instead of the 400 hp (298 kW) Wright R-975 Whirlwind radial engine.

The single BT-9D prototype led to the improved BT-14 which introduced a metal-covered fuselage and a 450 hp (336 kW) R-985-25 Wasp Junior engine and production of these for the USAAC totalled 251, of which 27 were later in 1941, fitted with an 400 hp (298 kW) R-985-11 engine and redesignated BT-14A.

Flight Training:

On the Eve of World War II
During the 1930s Depression the number of pilots the Air Corps trained decreased until 1937 only 184 graduated from advanced pilot training. Facing a resurgent German militarism and an aggressive Japanese military in 1939, the Air Corps planned to graduate 4,500 pilots in the following two years. Lacking facilities to train such a large number of cadets, in mid-1939 the Air Corps contracted with nine of the best civilian flying schools to begin training pilots. When France fell to Germany in 1940 the Air Corps increased the number of pilots to be trained to 7,000 per year. By December 1941 the Air Corps had contracted with 45 civilian flying schools and by 1943 the number increased to 63. In the first class at Randolph Field in 1939 only 257 pilots graduated. By the end of 1941 over 2,000 were enrolled in each class. At the end of World War II the Army Air Forces Training Command had graduated 250,000 pilots from its schools.

Training Fields Before World War II
During the 1930s the Army Air Corps conducted primary and basic flying training at Randolph and Brooks Fields, and advanced training at Kelly Field. These fields were just outside of San Antonio, Texas. In 1940 the Army Air Corps planned the expansion of pilot training and began offering basic flight instruction at additional fields. By 1944 there were 31 fields involved in basic training. Advanced training was originally given at Kelly and Brooks Fields; however, when the program expanded and was divided into single- and twin-engine instruction, other fields began to offer advanced instruction. Soon after, Brooks and Kelly Fields conducted only twin-engine training. Eventually, single- and twin-engine training fields spread across the country from coast to coast.

BT-9B SPECIFICATIONS
Span: 42 ft.
Length: 28 ft.
Height: 13 ft. 7 in.
Weight: 4,470 lbs. loaded
Armament: None
Engine: Wright R-975-53 of 400 hp.
Crew: Two - Instructor pilot and Student pilot
Cost: $20,000