The Republic XP-72 Wasp Major-powered "Super Thunderbolt" (or "Ultrabolt") was being developed in the latter part of World War 2 (1939-1945) as the ultimate incarnation of the war-winning P-47 Thunderbolt fighter/fighter-bomber (also produced by Republic). The XP-72 incorporated largely the same airframe with the massive, experimental Pratt & Whitney R-4360 "Wasp Major" series engine rated at 3,450 horsepower. As promising as the high-altitude fighter was becoming, the changing nature of the war ultimately found little need for such an aircraft. No more than two prototypes were produced.
As an expediency, the XP-72 made use of both the proven fuselage and wings of the P-47 before it. Some alterations to accommodate the large Pratt & Whitney were made to the airframe and this included a revised lower cowling to allow for proper aspiration of the engine. A large-diameter, four-bladed propeller unit was affixed to the powerplant. The aircraft was indeed considered the "Super Thunderbolt" when compared to the original P-47 offering.
The second prototype was given an Aero Products contra-rotating propeller arrangement (a pairing of three-bladed units to a single engine, equaling six total blades) and an estimated maximum speed of 550 miles per hour. Primary armament was to become an array of 6 x 12.7mm (.50 caliber) machine guns mounted in the wings (a reduction from the 8 x 12.7mm machine guns in the original P-47 Thunderbol). An alternative weapons loadout built into the contract was to allowed for 4 x 37mm autocannons in place of all of the machine guns. As secondary armament, the aircraft was to carry high-explosive rockets, 2 x 1,000lbs bombs, or 2 x fuel droptanks as needed at hardpoints under each wing.
Despite the performance gains and relatively easy development process, the conditions in the latter years of the war were such that all-new high-altitude fighters / interceptors were in little demand as existing types were more than enough to fulfill the role. The simple truth became that the XP-72 was no longer a needed commodity in the grand scope of the war - particularly with prop-powered aircraft reaching their technological apexes and turbojet technology beginning to take hold. As such, the two XP-72 prototypes were dropped from further development and scrapped by war's end along with cancellation of a production contract for 100 of the type. The XP-72 "Super Thunderbolt" would go down as just another of World War 2's "what-if" programs that failed to materialize any tangible fruits by war's end - leaving to the imagination what impact, if any, such powerful aircraft would have had if promptly adopted into operational service.
- X-Plane / Developmental
36.58 ft (11.15 m)
40.91 ft (12.47 m)
16.01 ft (4.88 m)
11,475 lb (5,205 kg)
17,494 lb (7,935 kg)
490 mph (788 kph; 425 kts)
41,998 feet (12,801 m; 7.95 miles)
1,200 miles (1,931 km; 1,043 nm)
5,000 ft/min (1,524 m/min)
6 x 12.7mm Browning M2 Heavy Machine Guns (HMGs) in wings.
4 x 37mm Automatic cannons in wings.
2 x 1,000lb bombs, Rockets, OR Fuel Drop tanks under the wings.
P-47 "Thunderbolt" - Production Series Designation of base P-47 design on which the XP-72 was built upon; 8 x 12.7mm machine guns.
XP-72 "Ultrabolt" - Prototype Series Designation; two examples constructed; 6 x 12.7mm machine guns; 1 x Pratt & Whitney R-4360-13 Wasp Major engine of 3,450 horsepower.