The Ki 43 Hayabusa (Oscar) went into production in late 1939 as the Army's fighter aircraft but only 40 were in service by the time of the Pearl Harbor attack.
5,919 Ki 43 type I through type III fighters were produced during the war and it was the most widely used fighter aircraft by the Japanese army air groups. It was designed by Nakajima's engineer Hideo Tonkawa
The Ki 43 had an operational range on its internal fuel tanks of 1095 miles and this could be extended to 1990 miles with the fitting of drop tanks, making it a suburb long range fighter interceptor aircraft.
The most encountered model was the Ki-43 type II which was powered by Nakajima's Ha-115-II Army Type 1 fourteen cylinder, twin row, air cooled, radial engine, rated at 1230 hp and able to attain a top speed of 358 MPH
It's main failing was that with only two 12.7 mm machine guns it was very under armed for air to air combat. with the introduction of the type II in November 1942 the pilot was protected by armor around the cockpit but the fuel tanks were not self sealing.
The Ki 43 Oscar was a very maneuverable aircraft and accounted for the most allied aircraft shot down during the war. In the hands of a skilled pilot it was a terrifying and worthily adversary.