In 1937,
Howard Hughes began the design of an advanced twin-engine,
twin-boom aircraft. The D-2's early gestation is historically obscure because Hughes Aircraft and its corporate successors have never released archives regarding the D-2; however, Howard Hughes had recently set a global circumnavigation speed record in a
Lockheed 14. Aircraft historian René Francillon speculates that Hughes probably initiated the project for another circumnavigation record attempt, but the outbreak of
World War II closed much of the world's airspace and made it difficult to buy aircraft parts without government approval, so he decided to sell the aircraft to the U.S. military instead. The first documentary evidence of the project is a December 1939 letter from Hughes to the
United States Army Air Corps (USAAC) proposing procurement of the D-2 and describing it as a "
pursuit type airplane". The design was somewhat similar to the
Lockheed P-38 Lightning that won the 1939 USAAC
interceptor aircraft design competition. Hughes later testified to the U.S. Senate that Lockheed had stolen his design, although this has been refuted by many. Rather than abandon the project, as he later recounted in the 1947 Senate investigation, he "decided to design and build from the ground up, and with my own money, an entirely new airplane which would be so sensational in its performance that the Army would have to accept it." Most of the airframe of the "DX-2" was made of
Duramold plywood, a plastic-bonded plywood molded under heat and high pressure. This material was advantageous from an aerodynamic and a metals-shortage standpoint, but was difficult to work, and rejected as insufficiently robust by the USAAC. Initially, the aircraft was to have been equipped with a
tail wheel but the landing gear was later changed to a
tricycle configuration with the main undercarriage units retracting rearwards into the twin booms and the nosewheel retracting rearwards and rotating 90 degrees to lie flat in the small central fuselage. The powerplants were to have been a pair of experimental
Wright R-2160 Tornado 42-cylinder, liquid-cooled radial engines. The D-2 was built in secret at the Hughes
Culver City, California factory with longtime associate,
Glenn Odekirk, providing engineering inputs. The secrecy further alienated USAAC officers, especially when Hughes denied
Materiel Command access to the plant. The USAAC had requested information about the project's progress, but did not enter into a formal contract until 1944. Final assembly and flight testing occurred at the Hughes Harper Dry Lake facility in the Mojave Desert. The finished D-2 looked like a scaled-up P-38 Lightning but, on paper, promised better performance; the USAAC repeatedly compared it to the
Lockheed XP-58 Chain Lightning. Difficulties encountered in obtaining the Wright Tornado engines led to the substitution of proven
Pratt & Whitney R-2800s. Numerous designations were given to the project, including D-2, DX-2, DX-2A, D-3, D-5, XA-37, and XP-73. The names reflected difficulties in development, shifting mission emphasis, and the USAAC's uncertainty over how to use the aircraft, which lacked both the maneuverability of a
fighter and the payload capacity of a
bomber or
attack aircraft. In June 1942, a
USAAF memorandum stated: "Hughes Model DX-2A. Has been submitted as a convoy protector, convoy destroyer, pursuit airplane, fighter, and light bombardment type. Its longest life has been as a convoy protector, but the latest specification which will be used in the negotiations calls it a fighter. If the present airplane is completed as a military weapon, it will have armament substantially as on the XP-58. Its sole claim to being a bomber is the fact that it is equipped with bomb bay doors. Since it is to be purchased in its commercial form ... it is considered advisable to call it the XP-73 for the sake of administering the contract." The XP-73 was thus a temporary designation applied to the D-2 after the Material Command at Wright Field obtained approval to purchase "one Hughes DX-2 airplane in present commercial form as a prototype ..." Within three days, the D-2 had been redesignated as the XA-37 for purposes of administering a contract. However, Materiel Command engineers vehemently opposed the aircraft, partly because it was built of wood instead of aluminum, and in part because they believed Hughes had not the managerial and industrial capability to actually produce the aircraft. Neither of the above
USAAF designations thus applied to any actual airplane; in the end, only two XF-11 prototypes and a mock-up were delivered. Because of Hughes's high political and public profile, the program was highly controversial. In July 1942, President
Franklin D. Roosevelt's requested information and progress from USAAF chief General
Henry "Hap" Arnold about the aircraft. Again in August–September 1943, the president and
White House staff discussed Hughes's progress with Arnold, who then gave the order to purchase 100 F-11 derivatives. ==Operational history==