After the surprise attack by Japanese naval forces on Pearl Harbor, Hawaii, in December of 1941 the United States officially entered World War 2. On June 30th, 1942, the Hughes design was still more or less in play and had been granted the official military experimental designation of "XP-73". Should the vehicle have gone into serial production, it would have attained the official production model designation of "P-73" as well as some sort of USAAC name. However, the following month, the Model D-2 was already being written in official USAAC papers as the "XA-37" for whatever reason - possibly for an attack-minded role as the "A-37".
As the war progressed, the USAAC was interested in all manner of war-making goods. While not completely sold on the idea of the Duramold process and a wooden fighter-bomber, it was an interesting alternative to an all-aluminum fighter, particularly under the resource stresses of war. Indeed, the British found considerable success with their de Havilland "Mosquito" fighter-bomber, nicknamed the "Wooden Wonder" for its heavy use of wood in its construction. Despite attempts by USAAC authorities to garner more information on Hughes' progress of the Model D-2, little information was made available by the company - the aircraft was developed under a huge veil of secrecy which hampered the issue of bringing the D-2 to light as a viable military platform. Hughes himself did not help matters but still funded the foundering project himself which helpful to the US military. When the D-2 program began to fall under threat from Material Division losing interest, Hughes pulled his political strings to remain in play. However, he passed on official government support so as to keep the D-2's development firmly in his own control.
Construction of the airframe continued under Hughes' direction though delays in the Wright Tornado powerplants forced Hughes to procure the lower-rated Pratt & Whitney R-2800-49 series instead. Another change to the arrangement was use of three-bladed propellers as opposed to the originally intended four-bladed types. The engines were also to benefit from a Hughes Aircraft-designed turbosurpercharger for increased performance. The aircraft was fully assembled - again, under secrecy - at Harpers Dry Lake, Muroc. The design had also finalized into a two-seat cockpit with intended pressurization for high-altitude work. The tail-dragger undercarriage was dropped in favor of the more forward-thinking tricycle arrangement. In this configuration, the Model D-2 was expected to top speeds of 445 miles per hour and feature a 1,000+ mile operating range under full combat load - though these were estimates.
In the spring of 1943, with the war in full swing, Hughes took to the controls of his D-2. At this point, the aircraft still lacked its in-house turbosuperchargers and cabin pressurization but scheduling called for ground runs of the system to which Hughes completed himself. However, the tests unveiled control issues which would have to be rectified for serious military consideration. The airframe's first formal flight was recorded on June 20th, 1943 and the control issues were ever more apparent to the point that the airframe would require a considerable modification, particularly at the wings. With little choice, Hughes engineers increased the span of the main wing assemblies, added flaps to the outboard areas and extended the trailing edges yet these changes would not entirely fix the problems and a more major redesign was in order.
At any rate, the Hughes D-2 was eventually dropped from all serious contention before the war had ended, its roles fulfilled by a bevy of other competing types. Beyond Hughes' own antics, the USAAC was not thoroughly convinced of the concept of an all-wood military plane in the age of metal ones. Additionally, there were questions as to the Hughes' commitment to his own project and the ability of Hughes facilities to produce the number of aircraft required of the war effort. The design was never fully cleared of its design flaws and the secrecy around the aircraft hurt USAAC chances of even seeing the in-development product. US Army interest in the product was over on August 13th, 1943.
Of all of the D-2's development, the aforementioned three-seat D-5 alternative held some military merit and three distinct forms were penciled out with the first being the dedicated light bomber form. A second model was intended to fulfill the role of escort fighter and feature a crew of two. To this was added a third model - a long-range, two-seat reconnaissance-minded platform lacking armament. It was this particular entry that struck a chord with US air power authorities for it was seeking such a platform for long-endurance reconnaissance work. The role was eventually shared by many converted fighter designs featuring photographic-reconnaissance equipment. The base D-5 design - apart from the unarmed reconnaissance version - was to incorporate a remote-controlled powered turret in the rear section of the fuselage nacelle, fitting 4 x 0.50 caliber Browning heavy machine guns for defense. The escort fighter form was to be further armed with 6 x 20mm cannons in the nose.
With so much work already completed on the D-2, Hughes Aircraft continued along the same route to develop a long-range reconnaissance platform for US military interest. This could prove particularly useful along the span of Pacific Ocean in the fight against the Japanese Empire. The singular D-2 prototype was lost to what was deemed a random "lightning strike" while in its hangar on November 11th, 1943. The design was resurrected, to an extent, in the upcoming Hughes product - the ill-fated and ultimately abandoned "XF-11" reconnaissance platform. The aircraft featured a similar twin-boom design and two prototypes were completed. One aircraft would nearly claim the life of Hughes himself while at the controls in his much-publicized crash. The XF-11 is detailed elsewhere on this site.