The promising nature of the Vought V-173 technology demonstrator produced a US Navy fighter contract for an expanded prototype form on June 30th, 1942. Engineer Charles Zimmerman had developed his wing-less "pancake" concept into the 1930s and was able to produce several scale models including the small V-162 test vehicle upon joining the Vought ranks as a consultant. From this came the V-173 which proved some of the concept sound, the design incorporating a circular fuselage with two leading-edge propeller engines and a centralized single-seat cockpit. Of course the military-grade version would require considerable modification and this made the follow-up XF5U something of a whole new beast.
The basic concept remained the same though structural dimensions were increased to accommodate more powerful engines, a new cockpit and fuselage as well as consideration for armament (this was to be a Navy fighter after all). The original 80-horsepower engines gave way to 2 x Pratt & Whitney R-2000-7 "Twin Wasp" radial piston engines of 1,350 horsepower each (driving four-bladed propellers). Dimensions included a length of 28 feet, 7 inches, a width of 32 feet, 6 inches and a height of 14 feet, 9 inches. Comparatively, the V-173 showcased a length of 26 feet, 8 inches, a width of 23 feet, 4 inches and an equal height. Loaded weights of both designs were notable, the V-173 topping the scales at 2,260lbs with the revised XF5U weighing 16,720lbs.The V-173 was also constructed of wood with fabric covering and sported a fixed undercarriage; the XF5U would be completed with a metal structure and metal skin as well as a retractable undercarriage. One of the more notable additions to the XF5U model was its inclusion of two circular intakes at the leading edges of the fuselage for aspirating the radial piston engines buried within the fuselage. As with the V-173, the XF5U relied on a network of shafts to drive its unorthodox engine installation.
US Navy authorities were already thinking ahead with their possible fleet of wingless aircraft. They envisioned a fighter-type entity with support for two external fuel drop tanks to counter the ranges required of over-sea travel. She would be capably-armed with either 6 x 0.50 Browning heavy machine guns or up to 4 x 20mm cannons. She was also intended for light bombing and provision for 2 x 1,000lb bombs were shortly added. The Navy looked for its new aircraft to reach a maximum speed of 500 miles per hour and out to ranges of 1,000 miles.
Vought was handed a contract to produce two airframes - one to serve as a static test bed and the other to become the full-fledged flyable platform. Vought returned with a wooden mockup which went under review by US Navy staff in June of 1943. This paved the way for a more finalized form appearing on June 25th, 1945. Testing of the "flyable" prototype revealed a host of technological issues primarily related to the powerplants (generally overheating) and the complicated gearbox arrangement which turned the flyable XF5U-1 into a recognized danger if pushed.
The war in Europe had drawn to a close in May of 1945 and the war in the Pacific followed in September. Many military programs were either shelved or scuttled altogether and the XF5U now fell under threat. Additionally, strides made in the realm of turbojet-powered flight further signaled the end for the propeller-driven, highly-novel XF5U. Its technological battle as well as ballooning program costs eventually led to its cancellation on March 17th, 1947. The two airframes were then subsequently scrapped, bringing an end to the "Flying Flapjack" endeavor of the US Navy.