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".
[N 1] 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.
The D-2 was built in secret at the Hughes Culver City, California factory with longtime associate, Glenn Odekirk, providing engineering inputs.
[citation needed] Difficulties encountered in obtaining the Wright Tornado engines led to the substitution of proven Pratt & Whitney R-2800s.
"[7] 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 ..."[8] Within three days, the D-2 had been redesignated as the XA-37 for purposes of administering a contract.
In July 1942, President Franklin D. Roosevelt's requested information and progress from USAAF chief General Henry "Hap" Arnold about the aircraft.
Hughes reluctantly concluded that the D-2 needed major modifications, including a complete redesign of the wings and a change in airfoil section.
He was lavishly entertained by Howard Hughes and his staff, and on 20 August he submitted to Arnold a glowing recommendation of the D-2 with photographic reconnaissance modifications.
[citation needed] It was this recommendation, shared by Elliott with his father the president, that caused General Arnold to verbally order the aircraft, overriding repeated objections from Materiel Command.
The following production variants of the D-5 were proposed by Hughes:[10] Data from McDonnell Douglas Aircraft since 1920: Volume II[11]General characteristics Performance