Many authors who write about American fighter aircraft of the World War 2 era state categorically that there never was a fighter project with the designation "P-73". For some obscure reason, this particular number seems to have been skipped. The aviation historian James Fahey claims that the P-73 designation was deliberately omitted as a result of political pressure applied to the Army by the Fisher Body Division of the General Motors Corporation. In 1942, Fisher was hoping to interest the Army in its new escort fighter design. At that time, the next available Army pursuit designation was P-73, but Fisher wanted the Army to assign to its new escort fighter a "nice symbolic number", something that would sound nice in advertising copy and would make for memorable slogans--something like "The French 75 in World War 1, the Fisher P-75 in World War 2" was envisaged. Fisher got its way and the Army agreed to assign the designation P-75 to its escort fighter project, the designations P-73 and P-74 being deliberately skipped.
However, a few other sources maintain that there really WAS a fighter aircraft designated P-73 and that it actually made some test flights. However, it was so secret that even today there are few details available about it. The P-73 was almost as mysterious in its time as the shadowy *Aurora* is today. However, the reason for all this secrecy was not any outstanding capabilities that the P-73 might have had, but was a result of the neurotic personality of the owner of the company which produced the aircraft. This was none other than the brilliant but eccentric movie tycoon, inventor, and industrialist Howard Hughes.
During the Second World War, many of the projects of the Hughes Aircraft Company were shrouded in secrecy and were the subject of mysterious and convoluted political maneuverings, due in no small part to the bizarre personality of its owner. Even though Howard Hughes and his company had been involved in several innovative aviation projects, the War Department found that dealing with Howard Hughes was a real nightmare. He could not be relied upon to meet schedules and his claims about the capabilities of his aircraft were often not credible. He would alternatively pressure the War Department into buying his aircraft right away without delay, then would withhold them from the government at the last minute. He had paranoid fears about others stealing his ideas, at one time claiming that Lockheed had stolen the idea for the P-38 Lightning from him.
Howard Hughes had always been obsessed with the setting of aviation records. In the mid-1930s, he had hired the talented aeronautical engineer Richard Palmer to build for him a racing monoplane designed specifically for the purpose of setting speed records. The product of this collaboration was the H-1B Racer, which took to the air for the first time on August 17, 1935. On September 13, 1935, Howard Hughes used his H-1B racer to set a world landplane speed record of 352.388 mph, a record which stood until 1939. in January 1937 he used an altered version of his same H-1B racing aircraft to set a transcontinental speed record of 7 hours 28 minutes 25 seconds (Burbank to Newark).
In July of 1938, Howard Hughes used a Lockheed 14-N2 twin-engined transport to set a round-the-world record of 91 hours 14 minutes flying time. Hughes believed that this record could be bested by a large margin if he could design and build an aircraft dedicated to the task of setting long-range records. This seems to have been the origin of the D-2, one of the most mysterious aircraft projects in all of aviation history. Even today, fifty years after the event, few details and even fewer photographs or drawings of the mysterious D-2 are publically available. They are presumably locked away somewhere in the vaults of the Summa Corporation, the holding corporation for the Hughes empire.
There is the possibility that Richard Palmer had begun work on the D-2 before he left Hughes to go to work for Vultee Aircraft, but this is not certain.
The D-2 project envisaged a twin-boom, twin-engined aircraft with a relatively small central crew nacelle. No effort was spared to minimize aerodynamic drag. The few drawings which are available show an aircraft with the same general configuration as the Lockheed P-38 Lighting, although appreciably larger and heavier. Most of the airframe of the D-2 was to be made of Duramold plywood, which was a plastic- bonded plywood molded under heat and high pressure. Initially, the aircraft was to have been a taildragger, but the landing gear was later changed to a tricycle configuration. The main undercarriage units retracted rearwards into the twin booms and the nosewheel retraced rearwards and rotated 90 degrees to lie flat in the small central fuselage. The powerplants were to have been a pair of Wright Tornado forty-two cylinder liquid-cooled radial engines.
The onset of war in Europe caused all thoughts of a record-breaking round-the-world flight to be abandoned. Aircraft engines and specialized aviation equipment urgently needed for rearmament were just not going to be made available for the sole purpose of setting records. In order to keep his project going, in December of 1939 Hughes offered to sell the drawings and data for the D-2 to the USAAC in the hopes of attracting a military contract. He hinted that the design might be made into a "pursuit-type airplane", although at that time the D-2 had no military role envisaged.
Hughes seems to have succeeding in interesting the Army in his project, since in 1940 the USAAC informed him that there was no objection to his purchase of a pair of Wright Tornado engines. However, the USAAF decided later to divert these Tornado engines to Lockheed for its XP-58 project, leaving Hughes without engines for his D-2. Hughes was forced to switch to a pair of Pratt & Whitney R-2800-49s for the D-2, and these engines arrived at Hughes in March of 1942.
Subsequent memos from Hughes to the Army seemed to indicate that he was changing his mind about the mission for the D-2. In May of 1940, he was no longer referring to a "pursuit-type aircraft", but instead to a "Duramold bombardment aircraft". The mission envisaged for the D-2 seems to have changed yet again in May 1941, the aircraft now being pictured as a bomber escort. In June of 1942, the USAAF seems to have referred to the aircraft as the "P-73" in one communique and as the "XA-37" in another, indicating that there was really no clearly defined military role for the aircraft. In reality, the D-2 could not carry enough bombs internally to make it a useful attack aircraft and was not sufficiently maneuverable to make it a useful fighter.
So it seems that the designation "P-73" was reserved by the Army at some stage for the fighter version of the D-2, and "XA-37" for the attack version. However, all of this is very murky, and it is not at all certain if the USAAF was ever very serious about the prospects for any useful military role for the Hughes aircraft. These designations may have been little more than place holders.
In early 1942, Hughes began to pressure the Army for a quick decision to purchase the D-2. Responding to this pressure, on June 16, 1942, Lt. Gen. H. H. Arnold, Commanding General of the USAAF, ordered Wright Field to acquire the D-2 from Hughes for testing as a prototype for possible future bomber development. However, a couple of weeks later, Hughes told the Army that he no longer wished to sell the D-2 to the Army but wished instead to test it himself first. The procurement of the D-2 was put on hold by the Army.
Components for the D-2 were built by Hughes at its Culver City plant, and final assembly was done at Harper Dry Lake in the Mojave Desert. Harper Dry Lake was an exceedingly remote area in the Desert, well away from prying eyes. The choice of this site was a reflection of Hughes' almost paranoid obsession with secrecy.
The D-2 was built primarily of wood. Power was provided by two 2000-hp Pratt and Whitney R-2800-49 radials driving three-bladed propellers. A hydraulic control surface boost mechanism was provided for elevators, rudders, and ailerons, one of the first applications of such a device to an aircraft. Turbosuperchargers and cabin pressurization were planned, but were not yet fitted. Crew was two or three.
Initial ground trials began in the spring of 1942. However, it soon became obvious that the control forces were excessively heavy when the boost mechanism was not operating. During high speed taxiing tests, Hughes briefly lifted the aircraft off the ground on some 30 occasions. These brief hops revealed some aileron instability, and further full-scale tests were delayed until new ailerons with broader chord were fitted.
The D-2 made its first true flight on June 20, 1943. Howard Hughes took it up twice that day. Hughes noted that there were rather high aileron control forces and that there was a tendency to roll with power on and with the undercarriage retracted. In order to correct these problems, Hughes increased the wingspan, but these changes did little to improve the flight characteristics.
Hughes reluctantly concluded that the D-2 needed major modifications, including a complete redesign of the wings and a change in aerofoil section. The wing center section, which was continuous through the fuselage nacelle, was to be revised to increase the size of the proposed bomb bay. Following these changes, the aircraft was to be assigned the company designation D-5.
On June of 1943, General Arnold noted that the lack of de Havilland Mosquito aircraft might result in an Army need for the Hughes design, and requested that the D-2 be flow to Bolling Field, DC. for inspection. At that time, the D-2 was undergoing modification to D-5 configuration and wasn't going anywhere. However, Hughes had the audacity to propose three separate production versions of the D-5--a two seat unarmed reconnaissance aircraft, a three-seat light bomber, and a two-seat escort fighter. The USAAF was not impressed, and recommended in August of 1943 that all development of the Hughes D-2/D-5 be discontinued.
In spite of the negative reception from the USAAF, Howard Hughes continued work on the D-2/D-5 on his own. In November 1944, while still undergoing modifications to the D-5 configuration, the D-2 was lost in a mysterious fire. According to Hughes, a "lightning bolt" struck the hangar in which it was being housed, and the aircraft was destroyed. By that time, the D-2/D-5 project had evolved into the XF-11, which was a long- range, high-speed unarmed reconnaissance aircraft of all-metal construction. It retained only the basic twin-boom/small central nacelle configuration of its predecessor.