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-cooledradial engine and had hydraulically actuated perforated splitflaps (dive brakes), and mainlanding gear that retracted backwards into fairing "trousers" beneath the wings.[1] The perforated flaps were invented to eliminate tail buffeting during diving maneuvers.[1]
The next iteration of the BT, theXBT-1, was equipped with a 750 hp (560 kW; 760 PS) R-1535. This aircraft was followed in1936 by theBT-1, powered by an 825 hp (615 kW; 836 PS) R-1535-94 engine. One BT-1 was modified with a fixedtricycle landing gear and was the first such aircraft to land on anaircraft carrier.
BT-1 of VB-5 in 1938
The final variant, theXBT-2, was a BT-1 modified to incorporate landing gear which folded laterally into recessed wheel wells,leading edge slots, a redesignedcanopy, and was powered by an 800 hp (600 kW; 810 PS)Wright XR-1820-32 radial.[1] 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 theDouglas 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.
The U.S. Navy placed an order for 54 BT-1s in 1936 with the aircraft entering service during 1938. BT-1s served onUSS Yorktown andEnterprise. 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."[2] It was also prone to unexpected rolls and a number of aircraft were lost in crashes.
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.[1]
Comparison between the XBT-1 (BuNo 9745) and XBT-2 (BuNo 0627) on 4 December 1936
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 asSBD-1 and SBD-2.
Douglas DB-19
One BT-1 (c/n346, BuNo 0643), the former BT-1S, was modified as the DB-19 which was tested by theImperial Japanese Navy as theDouglas DXD1 (long designation -Douglas Navy Experimental Type D Attack Aircraft)[1]
1 X as second letter is for experimental aircraft or imported technology demonstrators not intended for service,2 Hyphenated trailing letter (-J, -K, -L, -N or -S) denotes design modified for secondary role,3 Possibly incorrect designation, but used in many sources
