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Republic XP-72 "Superbolt": The P-47's Thunderbolt's Little Known Crescendo

Fighter planes are a bit like Pokemon. Before you pelt us with vegetables, allow us to explain. Fighter aircraft hone their abilities, then their engineers fine tune and modify these skills over time. Then, they evolve into something new entirely. Well, if the Seversky P-35 is like Pichu, and the P-47 Thunderbolt is Pikachu, the XP-74 is the full Raichu, with no debuffs whatsoever.
XP-72 8 photos
Photo: Republic Aviation
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The XP-72 was, for all intents and purposes, the ultimate evolution of the mighty Republic Thunderbolt, one of the toughest, deadliest piston fighters of World War II. Its Pratt & Whitney R-2800 Double Wasp engine could lug this 10,000 pound (4,536 kg) jug of an airframe up past 400 miles per hour (644 kph) and 42,000 feet (13,000 m) in the air.

It was also tough; it could shrug off flak and machine-gun fire barrages and still take its pilot safely back to base. All in all, the Thunderbolt is up there with the Spitfire and the Mustang as one of the most memorable aircraft from that era ever to fly. But as outstanding as the capabilities of the P-47 were, Republic engineers knew there was room for even more. More specifically, Republic engineer Alexander Kartveli knew there was room for improvement.

The Georgian-born engineer, as in the Eastern European Georgia, not Atlanta, had grand ideas for what the Thunderbolt's airframe was capable of. Firstly, while powerful and reliable, the iconic Double Wasp engine was a bit like last week's newspaper by 1944. Entertaining enough, but there was juicier stuff out there at this late stage in the Second World War.

The juicier engine selected for the upgraded Thunderbolt was the gargantuan 4,360c cubic-inch (71.489L) Pratt & Whitney R-4360-13 radial leviathan that made more power than most early jet engines. We're talking about upwards 3,500 horsepower. And to think it ran on regular aviation gas, and not jet fuel.

Republic XP\-72
Photo: Republic Aviation
With the engine paired with the Thunderbolt's airframe, the result was something Republic hoped would be twice as good as the P-47 it originates from. Speaking of Republic prototypes, the design team was also hard at work on the XP-69 high altitude fighter. A high-altitude fighter intended to feature a pressurized cockpit, perfect for shooting down German and Japanese bombers at heights above 30,000 feet (9,144 meters).

Ultimately, it was the mildly more conventional XP-72 that was chosen to commence production. An order of as many as 100 airframes was thought to be on the table between the Farmingdale, New York, based Republic Aviation and the Army Air Corps. The finished product had a very similar silhouette compared to the base P-47. But closer inspection reveals a tougher, beefier aircraft, with an enormous quad-bladed propeller that swallowed huge swaths of air through themselves as they dragged this 14,433 pound (6,560 kg) airframe all the way to an estimated top speed of 490 to 500 miles per hour at service altitude.

In the second built prototype, the prop arrangement switched to a wicked-looking contra-rotating dual prop configuration. Armament was slated to be one of three configurations. You'd find either the eight browning machine guns in the average P-47D, a set of four M4 37 mm autocannons, or a third configuration using a mix of machine guns and autocannons with two M4s and four M2s in each wing. Such a powerful airplane could have gone toe to toe with the best variants of Axis fighters in service during the period, including the German Bf-109G, Fw 190 A-5, and the Japanese A6M5 Zero and N1K-J Shiden.

Republic XP\-72
Photo: Republic Aviation
It's almost a guarantee that an airplane of this caliber could be a difference-maker in a potentially long and dragged-out tail end of the war. That is, if not for a couple of big problems. For one thing, the priorities of the U.S. Army Air Corps had changed somewhat since 1941. By late 1944, P-51D Mustangs and British Mosquito fighters were already escorting hoards of bombers from the American Eighth Air Force into the heart of Germany.

With Dresden, Berlin, Stuttgart, Hamburg, and just about every other German city of any significance in ruins, and with Imperial Japan soon to follow, there simply wasn't a need for a point defense interceptor the likes of which fought, for example, in the Battle of Britain. But on top of all of that, right around the time the XP-72, colloquially called the Superbolt by enthusiasts, took to the skies, the Lockheed P-80 Shooting Star jet fighter had already made its first test flight.

Regardless of whether or not the Axis forces surrendered by the end of 1945 or not, the writing was already on the wall for the twilight of the piston-engined fighter. As such, the production order for the Superbolt was canceled.

From then on, Republic set about building the admittedly excellent F-84 Thunderjet instead. The fate of the two only prototypes remains a mystery to this day.

Republic XP\-72
Photo: Reddit
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