Throughout World War 2 (1939-1945), the United States Navy pushed its ever-growing stable of carrier-based aircraft to all-new heights, branching from dedicated fighters to include an inventory stocked with versatile fighter-bomber types and even more dedicated, advanced bombing platforms in the dive and torpedo bomber molds. As American carriers grew in size, they were able to accept larger aircraft on their stronger, more spacious decks and one of the most famous of these large aircraft to emerge at the end of the war became the storied Douglas A-1 "Skyraider" of 1946 (detailed elsewhere on this site).
Back in 1942, the Midway-class carrier was in development and this design brought about the flexibility for Navy warplanners to include larger aircraft designs on the planned deck space. Authorities initially approached a design with a twin-engine configuration for the power necessary to undertake the torpedo bomber role with reconnaissance and level bombing capabilities as secondary. The design would be able to carry several torpedoes into battle, broadening the tactical appeal of the torpedo bomber when compared to wartime contemporaries (these limited to a sole torpedo).
During November of 1942, the United States Navy (USN) contracted with Douglas Aircraft Corporation to design, develop, and produce their new bomber. The project received the necessary steam to forge ahead in late October 1943 when a contract was signed for two flyable prototypes (the second to receive a slightly lengthened fuselage) and a static testbed to be designated "XTB2D-1" under the name of "Skypirate".
The twin-engine approach was ultimately dropped as Douglas engineers (a team that included famous American aviation engineer Ed Heinemann) went to work, instead utilizing a single-engine approach of considerable power. This became the Pratt & Whitney XR-4360-8 supercharged radial piston engine of 3,000 horsepower driving a pair of 14.3-foot diameter, four-bladed propeller units in a contra-rotating fashion. An internal bomb bay was part of the original design plans as well while a rear turret would be used to defend against trailing aerial threats. A rather modern tricycle undercarriage was fitted to allow the large blades the necessary clearance while also simplifying ordnance loading/reloading. The nose leg featured a telescoping strut to reduce its length when retracted into its bay as well as a twin-wheel configuration to contend with the rigors of carrier deck service. A three-man crew would operate the various onboard systems and their stations were fully armored for low-altitude combat flying. The tail unit relied on a single, large-area rudder complimented by very low-mounted horizontal planes. This section also carried the arrestor gear.
The wing mainplanes were given considerable attention during the design phase. They folded outboard of the main landing gear legs for optimal carrier storage and fuel was stored across four major compartments inboard and outboard of the legs. Each wing held two hardpoints for carrying 2,100 lb torpedo loads (or conventional drop ordnance equivalent). Outboard hardpoints were further plumbed for jettisonable fuel tanks which could be used to increase operational ranges. Each wing was also outfitted with 2 x 0.50 caliber Browning M2 heavy machine guns for forward strafing of ground targets. Full-span slotted flaps, automatically adjustable in flight and inboard sections doubling as ailerons, and an anti-icing feature were also part of the rather advanced design.
The Firestone company provided the dorsal turret works which installed 2 x 0.50 caliber M2 Browning heavy machine guns. The turret was fitted at the middle of the aircraft with the cockpit ahead. A ventral structural fairing was planned below and this station was to showcase an observation window as well as remotely-controlled 2 x 0.50 caliber Browning M2 heavy machine guns fixed to fire rearwards with a limited elevation span.
Inspection of a mockup was given in early 1943 as the war in Europe and the Pacific raged on. Sufficiently impressed, the Navy service awarded Douglas a contract for twenty-three aircraft based on the work displayed. However, the program continually suffered delays and general disinterest as propulsion gear was slow to be delivered and serial production not ready heading into the middle of 1944. Some development on the design did continue for a Skypirate prototype finally made it airborne on March 13th, 1945 - though this airframe lacked its dorsal turret and ventral fairing.
By this time, Japanese naval superiority was long gone and the fighter-bombers aboard existing American carriers proved more than sufficient to content with a dwindling enemy presence by the summer of 1945. With little need for such a large and expensive combat system, the XTB2D project faltered mightily. It was given its death blow with the Japanese surrender in August of 1945. What little testing had been completed on the Skypirate showcased issues with the wings, engines, and propellers and only added to the program's woes. While some thought was given to modifying the Skypirate as a dedicated long-range, high-altitude reconnaissance platform and even as a jet testbed, neither scenario panned out, signaling the formal end of the Skypirate project in 1947.