The Nakajima Ki-43 Hayabusa (Peregrine Falcon) was the most modern fighter available for the IJAAF at the start of the war and it caused an unpleasant surprise to those Allied pilots who first flew against it. Although it appeared weak and underpowered, it was highly maneuverable and could outmatch the Hurricanes and Buffaloes it encountered early in the campaigns in Southeast Asia. However, this maneuvrability was achieved at the expense of armor protection and self-sealing fuel tanks in the early variants (deficiencies corrected in later versions) which made it easy prey once more substantial opposition was encountered. Ki-43s were used throughout the entire war despite its obvious obsolecence after 1943 and the introduction of its successor, the Ki-84, as it was the most widely produced IJAAF fighter and the aircraft of choice for Army aces like Shinohara (54 kills) and Anabuki (51 kills). They were also used as kamikazes and by French and Indonesian forces post-war.

The Ki-43 was the result of a 1937 design and was first flown in January 1939. The aircraft entered production as the Ki-43-I with a number of subvariants (Ki-43-Ia, -Ib and -Ic) different only in their armament configuration. Initial variants lacked protection, this was solved somewhat rudimentarily in later versions beginning with the Ki-43-II which also featured a more powerful engine, clipped wings and a redesigned canopy. Lastly, the Ki-43-IIIa incorporated a new powerplant but still suffered from poor armament something which was later addressed in the Ki-43-IIIb interceptor which was unfortunately developed too late to see action.