It featured fully retractable landing gear, flush riveting, and most significantly a Pratt & Whitney R-1830-SC2G engine with a belly-mounted turbo-supercharger, producing 1,200 hp (890 kW) and good high-altitude performance.

The turbo-supercharger had been refined by Boeing as part of the development program for the B-17 Flying Fortress, and the improved performance it offered was of great interest to other aircraft manufacturers.

[1] The XP-41 and sole AP-4 were nearly identical, although the AP-4 was initially fitted with a large prop spinner and a tight-fitting engine cowling, as a testbed to evaluate means of improving the aerodynamics of radial-engined fighters, following similar experiments with the first production P-35.

The aircraft was powered by an R-1830-35 14-cylinder air-cooled radial engine with a General Electric B-2 turbo-supercharger generating 1,200 hp and driving a three-blade variable-pitch propeller.

Early testing revealed a strong tendency to yaw during takeoff and landing rolls, fixed by redesigning the tailwheel.

Although the aircraft exceeded the initial USAAC performance requirements, by 1941 it was clearly obsolete, lacking maneuverability, armor, or self-sealing fuel tanks.

The USAAC felt the basic P-35/P-43 design had exhausted its reserves for further improvement in performance and shifted its interest to the promising Republic P-47 Thunderbolt.

Ongoing delays in the P-47 program resulted in USAAC ordering an additional 80 P-43A, with Pratt & Whitney R-2180-1 Twin Hornet engine rated at 1,400 hp (1,000 kW).

An additional 125 P-43A-1s were ordered for China through the Lend-Lease program, originally intended to equip the Third American Volunteer Group (AVG).

Apparently, several AVG pilots asked Chennault to keep some P-43s, but the request was denied due to the aircraft's lack of armor or self-sealing fuel tanks.

On the other hand, in April 1942, veteran CAF fighter pilot Maj. Zheng Shaoyu, a survivor of many air battles including the "Zero-scourge" in the war against the Imperial Japanese invasion of China, was ferrying a P-43 back into China for renewed combat operations against the Japanese, when it suddenly caught fire causing his death in the ensuing crash.