Late-war Douglas successors to the Dauntless and Devastator, part 2: TB2D Skypirate

In my previous post on late-war carrier-based Douglas attack aircraft, I discussed in brief detail the fact that the Douglas TBD Devastator was the US Navy's first monoplane torpedo bomber and the first-ever all-metal aircraft to enter service, but also the first with a completely enclosed cockpit, considering that previous American torpedo bomber aircraft were open-cockpit, all-wood biplanes, but also the fact that the Devastator itself was becoming obsolescent on the eve of the Pearl Harbor attack and had the poor combat performance at the Battle of Midway largely thanks to the technical inadequacies of the Mark 13 torpedo the Devastator was designed to carry. As the TBD Devastator was eventually retired from active combat service after Midway, the Grumman TBF/TBM Avenger took up the combat roles for which the TBD had been designed, playing a pivotal role in the air and sea engagements during battles off the east coast of the Philippines with the Imperial Japanese Navy in late 1944 to early 1945 by sinking the Japanese warships Musashi and Yamato. Although the Avenger formed the backbone of the Navy's torpedo bomber force in the wake of the Battle of Midway, the Battle of Midway was not the end of the road for the development of torpedo bomber aircraft by Douglas. The second and final post of my two-part series on replacements for the Dauntless and Devastator will now concentrate on discussion of Douglas design efforts at creating a successor to the TBD Devastator, which culminated in the XTB2D Skypirate.

Douglas D-295 proposal to the SD-114-6 competition (as of mid-1939) 

In March 1939, the US Navy issued the SD-114-6 requirement for a new three-seat torpedo bomber to replace the TBD Devastator. The crew of this aircraft comprised a pilot, co-pilot/bombardier, and radio operator/gunner, and the proposed aircraft would have a range of 1,000 miles (1,609 km) with 1,500 lb (681 kg) of bombs or one torpedo, a service ceiling of 30,000 feet (9,144 meters), and a gross weight of 12,500 lb (5,670 kg). By August 24, six manufacturers (Brewster, Douglas, Grumman, Hall Aluminum, Vought, and Vultee) had submitted bids for the SD-114-6 competition. The Douglas submission, which bore the company designation D-295, was an improved derivative of the Devastator featuring a single Wright R-2600 Twin Cyclone radial engine, a length of 38 feet 1.75 in (11.63 meters), a wingspan of 47 feet (14.33 meters) (29 feet [8.84 meters] when folded), and armament comprising two 20 mm cannons in the wings, two machine guns on the nose fuselage behind the fuselage, and bombs stowed in the fuselage. In the end, the Navy selected the Grumman and Vought proposals for production, designating them TBF and TBU respectively.

US Navy Bureau of Aeronautics Standard Aircraft Characteristics (SAC) sheet for the Douglas XTB2D-1 Skypirate

Douglas lost the first round in terms of a proposed successor to the TBD Devastator, but it eventually had better luck next time when in February 1942 the US Navy announced a requirement for a large torpedo-scout-bomber. In March 1942, Douglas carried out a series of design studies in response to the VTSB requirement under the designation D-544, culminating in eight different designs, whose weights ranged from 21,000 lb (9,571 kg) to 23,500 lb (10,660 kg). The first three designs featured twin-engine aircraft powered by two Wright R-1820 Cyclone radial engines, and two more had one turbocharged Allison V-3420 liquid-cooled V-cylinder engine in the rear fuselage behind the pilot, the first with a four-blade propeller connected to the engine by a long shaft, and the second with a three-blade propeller ahead of each wing leading edge and connected by angle extension shafts. The last three D-544 design studies were powered by one Pratt & Whitney R-4360 Wasp Major radial engine driving four-blade counter-rotating propellers, of which two had twin vertical stabilizers and the third had a one vertical stabilizer. The Navy's Bureau of Aeronautics eventually opted for the Wasp Major-powered D-544 proposal with a single-tail, and a contract was placed in November for two prototypes (BuNos 036933 and 036934), which were designated XTB2D-1. The design was originally called Devastator II, but later on Douglas changed the aircraft's name to Skypirate.

Top: First XTB2D prototype (BuNo 036933) on the tarmac, early 1945.
Bottom left: First XTB2D-1 prototype (BuNo 036933) landing after a test flight
Bottom right: Second XTB2D-1 (BuNo 036934) in flight 

The XTB2D-1 was 46 feet (14.02 meters) long, with a wingspan of 70 feet (21.34 meters) (36 feet [10.97 meters] when folded), a height of 22 feet 7 in (6.88 meters), a wing area of 605 square feet (56.265 square meters), a gross weight of 34,760 lb (15,767 kg), a loaded weight of 28,545 lb (12,948 kg) with torpedoes, a range of 1,250 miles (2,011 km), a service ceiling of 27,900 feet (8,504 meters), and a top speed of 340 miles per hour (547 km/h). Armament comprised seven 0.50 in (12.70) machine guns and 8,000 lb (3,629 kg) of bombs or four torpedoes. The Skypirate itself was intended to operate from the new Midway-class aircraft carriers as well as the Essex-class carriers. A full-scale mock-up of the XTB2D-1 design was inspected in March and May 1943, and an order was also placed for 23 pre-production aircraft (BuNos 89097/89119). Although the XTB2D-1 had minimal support from the Navy and the Navy itself recommended cancelling the program on May 20, 1944, Douglas slowly proceeded with construction of the Skypirate prototypes. The first of the two XTB2D-1 prototype flew on March 13, 1945, while second prototype followed in the summer of that year, but by this time Japanese forces in the Pacific were collapsing quickly and the Midway-class carriers encountered delays in preparations for entering commission with the US Navy. Hence, the pre-production order for the XTB2D Skypirate was cancelled and test flights of the aircraft were suspended, with both aircraft being scrapped in 1948. Back in November 1944, Douglas had proposed to fit the XTB2D-1 with an auxiliary turbojet in place of dorsal turret, but this scheme did not materialize.

[EDIT: It has come to my attention that a Douglas company projects index lists company designations D-295, D-298, and D-306 as torpedo bomber designs from the first half of 1939. The D-306 is listed in the index as an export variant of the D-298, however, so the D-298 and D-306 are probable company designations for the TBD-1A floatplane version of the TBD Devastator. Since D-295 is listed as being a torpedo bomber and issued in May 1939, two months after the SD-114-6 requirement was issued, it is almost certain that D-295 was the company designation for the Douglas submission for the SD-114-6 specification.]

References:

Buttler, T., and Griffith, A., 2015. American Secret Projects 1: Fighters, Bombers, and Attack Aircraft, 1937 to 1945. Manchester, UK: Crecy Publishing. 

Kowalski, B., 1996. Douglas XTB2D-1 Skypirate. Simi Valley, CA: S. Ginter.