The Northrop BT was an American two-seat, single-engine monoplane dive bomber built by the Northrop Corporation for the United States Navy. At the time, Northrop was a subsidiary of the Douglas Aircraft Company. While unsuccessful in its own right, the BT was subsequently redesigned into the Douglas SBD Dauntless, which would form the backbone of the Navy's dive bomber force. Design and development The design of the initial version began in 1935. It was powered by a Pratt and Whitney XR-1535-66 double row air-cooled radial engine and had hydraulically actuated perforated split flaps (dive brakes), and main 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 R-1535. This aircraft was followed in 1936 by the BT-1, powered by an 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. 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 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. Operational history The U.S. Navy placed an order for 54 BT-1s in 1936 with the aircraft entering service during 1938. BT-1s served on and . 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. Variants XBT-1 Prototype, one built. BT-1 Production variant, 54 built. BT-1S 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. XBT-2 One BT-1 modified with fully retractable landing gear and other modifications. BT-2 Production variant of the XBT-2, 144 on order completed as SBD-1 and SBD-2. Douglas DB-19 One BT-1 (c/n346, BuNo 0643),