The design of the initial version began in 1935. It was powered by a 700 hp (520 kW; 710 PS) Pratt and Whitney XR-1535-66 double row air-cooled radial engine and had hydraulically actuated perforated split flaps or "dive-brakes" and a landing gear that retracted backwards into fairing "trousers" beneath the wings. The perforated flaps were invented to eliminate tail buffeting during diving maneuvers.
The next iteration of the BT, the XBT-1, was equipped with a 750 hp (560 kW; 760 PS) R-1535. This aircraft was followed in 1936 by the BT-1, powered by an 825 hp (615 kW; 836 PS) R-1535-94 engine. One BT-1 was modified with a fixed tricycle landing gear and was the first such aircraft to land on an aircraft carrier.
BT-1 of VB-5 in 1938
The final variant, the XBT-2, was a BT-1 modified to incorporate landing gear which folded laterally into recessed wheel wells, leading edge slots, a redesigned canopy, and was powered by an 800 hp (600 kW; 810 PS) Wright XR-1820-32 radial. The XBT-2 first flew on 25 April 1938 and after successful testing the Navy placed an order for 144 aircraft. In 1939 the aircraft designation was changed to the Douglas SBD-1 with the last 87 on order completed as SBD-2s. By this point, Northrop had become the El Segundo division of Douglas aircraft, hence the change.
BT-1 at El Segundo
VB-5 lineup of BT-1s
The U.S. Navy placed an order for 54 BT-1s in 1936 with the aircraft entering service during 1938. BT-1s served on USS Yorktown and Enterprise. The type was not a success in service due to poor handling characteristics, especially at low speeds, "a fatal flaw in a carrier based aircraft." It was also prone to unexpected rolls and a number of aircraft were lost in crashes.
Prototype, one built.
Production variant, 54 built.
A BT-1 (c/n346, BuNo 0643) was fitted with a fixed tri-cycle undercarriage. This aircraft was damaged in a crash on 6 February 1939, returned to Douglas and repaired to BT-1 standard.
Comparison between the XBT-1 (BuNo 9745) and XBT-2 (BuNo 0627) on 4 December 1936
One BT-1 modified with fully retractable landing gear and other modifications.
Production variant of the XBT-2, 144 on order completed as SBD-1 and SBD-2.
One BT-1 (c/n346, BuNo 0643), the former BT-1S, was modified as the DB-19 which was tested by the Imperial Japanese Navy as the Douglas DXD1 (long designation - Douglas Navy Experimental Type D Attack Aircraft)