Late-war Douglas successors to the Dauntless and Devastator, part 1: SB2D and BTD Destroyer

During World War II, the El Segundo Division of Douglas built a number of attack aircraft designed to take out Japanese warships in the Pacific with either bombs or torpedoes, including the SBD Dauntless dive bomber and TBD Devastator torpedo-bomber. The SBD Dauntless played a pivotal role in the US Navy victory at the Battle of Midway in June 1942 by sinking the Imperial Japanese Navy's four fleet carriers and heavy cruiser Mikuma, effectively dashing Japan's hopes of conquering the Hawaiian Islands and putting the Japanese military on the defensive by forcing Japan into retreat in the western Pacific. As the Pacific theater of World War II progressed, however, the Curtiss SB2C Helldiver took over the roles that the Dauntless had performed, and the June 1944 Battle of the Philippine Sea would be the last battle involving the SBD. The TBD Devastator was one of the first American monoplane torpedo bombers and the most advanced US Navy attack aircraft at the time of its deployment, designed to pack a devastating wallop against enemy warships when traveling at high speed, but it fared poorly in the Battle of Midway due to defects with the torpedo it was design to carry and lower speed and maneuverability compared to the Mitsubishi Zeroes. I finally got to see the Dauntless in person when I visited the USS Midway carrier museum in San Diego, and the Planes of Fame Museum and Yanks Air Museum in Chino. Although no Devastators are preserved in museums, several TBDs survive intact underwater, pending recovery and possible restoration for eventually display. However, a replica of the TBD Devastator was built for the 2019 film Midway and has since been put on display in the Hangar Section of the USS Midway Museum; I saw the TBD replica during a visit to the carrier museum last June. However, lost in talk of US Navy attack plane development in World War II is the fact that in 1943-1945, Douglas developed a number of new-generation attack aircraft to replace the SBD and TBD. For all purposes and intents, the first post in a two-part discussion about late-war Douglas attack aircraft for the US Navy will center upon the SBD's slated successor, the SB2D/BTD Destroyer.       

Douglas SBD Dauntless (BuNo 28536 shown here, photographed by me at the Planes of Fame Museum in Chino, California in April 2019), the aircraft that the SB2D/BTD Destroyer was designed to replace. 

On February 3, 1941, the US Navy's Bureau of Aeronautics (BuAer) issued a Request for Proposals for a new dive bomber to supplant the Douglas SBD Dauntless and Curtiss SB2C Helldiver. In response, Ed Heinemann, the chief designer at the El Segundo Division of Douglas responsible for design of the Dauntless, envisaged a design for a dive bomber featuring a laminar flow gull-wing, a bomb bay and underwing racks for up to 4,200 lb (1,900 kg) of bombs or one torpedo (typically the Mark 13), and defensive armament comprising two wing-mounted 20 mm (0.79 in) cannon and two remote-controlled turrets, each with two .50 in (12.7 mm) machine guns. For its part, Curtiss' submission was similar in landing gear configuration and size, and it had an internal bomb bay for carrying up to 4,000 pounds (1,800 kg) of bombs, or alternatively, two torpedoes in semi-submerged mountings, plus hardpoints for two 500-pound (230 kg) bombs fitted under the wings, while defensive armament comprised six .50-caliber machine guns or four 20 mm cannon in the wings. Both proposals possessed a tricycle landing gear, a feature not seen in the Navy's operational carrier-based planes, and power was to be supplied by one Wright R-3350 Duplex Cyclone radial engine delivering 2,300 hp (1,700 kW). On June 20, the Navy placed a contract for two prototypes (BuNos 03551/03552) of the Douglas proposal, which was designated XSB2D-1. Meanwhile, the Curtiss design was designated XSB3C-1 and two prototypes (BuNos 03743/03744) were ordered after a mock-up inspection in December, but the Navy eventually judged the Curtiss design inferior to the Douglas aircraft in performance, so the XSB3C program was cancelled in 1942. 

Left: Douglas XSB2D-1 (BuNo 03551) in flight
Right: Douglas BTD-1 Destroyer (BuNo 04963) in flight, July 25, 1944

The first of the two XSB2D-1 prototypes flew on April 8, 1943. Despite being heavier and more complex than the Dauntless, the XSB2D was deemed to have better performance with the capability to carry a bigger bombload, and the Navy placed an order for 358 SB2D-1s (BuNos 04959/04971 and 09048/09384). By June, however, the Navy was shifting away from multi-seat dive bombers and focusing on a single-seat dive bomber designed to combine the combat capabilities of the SBD and SB2C with the strengths of a torpedo bomber, introducing the new BT (Bomber-Torpedo) category. Douglas immediately reworked the SB2D design into a single-seat dive/torpedo bomber to meet the Navy's new requirement, dispensing with the turrets and second crewmember, adding more fuel and armor, and equipping the wing racks with two torpedoes instead of one. This design was given the designation BTD-1 by the Navy and christened the Destroyer, and all orders for the SB2D-1 were converted to the BTD-1. The first flight of the BTD-1 occurred on March 5, 1944. but the Destroyer turned out to be heavier than the XSB2D-1 prototypes and had poorer performance, so Ed Heinemann asked the US Navy to cancel the BTD program. However, the Navy did not heed Heinemann's offer and still went ahead will full-scale production of the Destroyer, with deliveries to the Navy beginning in June 1944, and 28 BTD-1s were built before the end of World War II led to the remaining BTD-1s on order being canceled. Two BTD-1s (BuNos 04962 and 04964) were modified to house one 1,500 lb (6.7 kN) thrust Westinghouse 19B turbojet in the rear fuselage and designated XBTD-2, with the first flight occurring in May 1944. However, the turbojet did not deliver the expected improvement in performance because the Westinghouse turbojet underperformed at speeds of more than 200 miles per hour. Only the first XBTD-2, while second never flew. None of the BTDs saw combat in the Pacific theater of World War II, mainly being used for training purposes until 1947. In any case, by the time that the BTD went into production, Heinemann and his team were working on a dedicated dive/torpedo bomber entirely from scratch, the XBT2D-1, which would later become the AD/A-1 Skyraider.

Paradoxically, even though the SB2D/BTD Destroyer did not live up to its original goal of supplanting the SBD Dauntless in operational service due to changing requirements, at least it happened to be one of a few little-known US military aircraft of World War II that went into production (alongside the Consolidated B-32 Dominator and General Motors P-75 Eagle). That said, the mission philosophy for the BTD would eventually find its way into the Douglas AD/A-1 Skyraider and Martin BTM/AM Mauler, both of which were the last carrier-based tactical bombers to use piston power.