The Republic P-43 was a single-engine, all-metal, low-wing monoplane fighter aircraft first delivered in 1940 to the United States Army Air Force.

The Seversky Aircraft Company, which in 1939 changed its name to the "Republic Aviation Company", constructed a range of one-off variants of its Seversky P-35 design that featured different powerplants and enhancements, with the designations "AP-2", "AP-7", "AP-4" (which flew after the AP-7), "AP-9", XP-41; and actually built a carrier-based version designated the "NF-1 (Naval Fighter 1)".

None of these variants went into production and are of little interest, but the AP-4 proved significant in the further development of Seversky aircraft. It featured fully retractable landing gear, flush riveting, and most significantly a Pratt & Whitney R-1830-SC2G engine with a belly-mounted turbo-supercharger, offering 1,200 horsepower (890 kW) and good high-altitude performance. The exhaust-driven turbosupercharger had been refined by Boeing as part of the development program for the B-17 bomber, and the opportunities offered by it for improved performance were of great interest to other aircraft manufacturers.

The one AP-4 built was used as a test platform to evaluate means of improving the aerodynamics of radial-engine fighters. It was fitted with a very large prop spinner and a tight-fitting engine cowling, following similar experiments that had been performed with the first production P-35. The AP-4's big spinner was later removed and a new engine tight cowling was fitted. Unsurprisingly, these measures led to engine overheating problems. On March 22 1939, the engine caught fire in flight, the pilot had to bail out, and the AP-4 was lost.

Despite its final loss, the USAAC liked the turbo-supercharged AP-4 demonstrator enough to order thirteen more in May 1939, to be designated "YP-43". However, USAAC requirements led to many modifications, and the YP-43 ended up looking much different from the AP-4.

The YP-43 was powered by a P&W R-1830-35 14-cylinder Twin Wasp radial engine with turbo-supercharger, offering 1,200 horsepower (890 kW) and driving a three-blade propeller. Armament consisted of two 12.7 mm machine guns in the nose, plus a single 7.62 mm machine gun in each wing. The cockpit scheme was revised, leading to a distinctive "razorback" configuration, as it would later be called.

The first of the thirteen YP-43s was delivered in September 1940, and the last was delivered in April 1941 when the USAAC planned to purchase Republic's proposed successor design, the P-47B. However, delays occurred in the XP-47B program, so the Air Corps another batch of 80 "P-43As", with a slightly different engine fit. Further delays led to yet another order for 125 "P-43A-1s" intended as Lend-Lease aircraft for China, with this last batch featuring armament of four 12.7 mm machine guns and self-sealing fuel tanks.

Specifications (variant described)

General characteristics

• Crew:
• Capacity:
• Length: m ( ft)
• Wingspan: m ( ft)
• Height: m ( ft)
• Wing area: m² ( ft²)
• Empty: kg ( lb)
• Loaded: kg ( lb)
• Maximum takeoff: kg ( lb)
• Powerplant: Engine type(s), kN (lbf) thrust or
• Powerplant: Engine type(s), kW ( hp)

Including the thirteen YP-43As, a total of 272 P-43s of all types were delivered by the time of the last delivery in March 1942. The ultimate fate of all these aircraft is a bit fuzzy, mostly because the "Lancer", as it was known, was so forgettable. At least 51 did make it to China, and some served with Claire Chennault's American Volunteer Group, the "Flying Tigers".

In combat, the P-43 due to its turbo-supercharger enjoyed much better high-altitude performance than the Curtiss P-40 that was the mainstay of the Flying Tigers. The P-43A was faster than the P-40E above 6 km, and had a much better climb rate above 3 km, too. To capitalize on its strenghts, the few available P-43s were often used as top cover for the P-40 fighters.

However, the P-43's turbo-supercharger was unreliable, the tanks were prone to leak, and as the P-43's R-1830 engines were in high demand by the numerous Douglas C-47 transports in the theatre, they were grounded rather quickly, leaving only the obsolescent P-40 to deal with the latest Japanese high-performance fighters like the Nakajima Ki-44.

Most of the P-43s that were not sent to China were converted into photo-reconnaissance aircraft, and a handful of these photo-reconnaissance Lancers were provided to Australia. These aircraft appear to have been given designations such as "P-43B", "P-43C", and "P-43D", with all then redesignated "RP-43" (where the "R" stood for "restricted from combat") in the fall of 1942, but the details are unclear. The type saw little combat in any capacity. The P-43's only real significance was as a stepping stone to something better, and a way of keeping Republic's production lines going until they could deliver the new XP-47B.

Designation sequence: P-40 - XP-41 - XP-42 - P-43 - P-44 - XP-45 - XP-46 - P-47

• Republic P-43 Lancer in Chinese service