It was the world's first low-wing monoplane shipboard fighter to enter service[note 1] and the predecessor of the famous Mitsubishi A6M "Zero".

[4] The resulting design, designated Ka-14 by Mitsubishi, was an all-metal low-wing fighter, with a thin elliptical inverted gull wing and a fixed undercarriage, which was chosen as the increase in performance (estimated as 10% in drag, but only a mere 3% increase in maximum speed) arising from use of a retractable undercarriage was not felt to justify the extra weight.

[4] The second prototype was fitted with a revised, ungulled wing, and after various changes to maximize maneuverability and reduce drag, was ordered into production as the A5M.

With the Ka-14 demonstrating excellent performance, the Imperial Japanese Army Air Force ordered a single modified prototype for evaluation as the Ki-18.

While this demonstrated similar performance to the Navy aircraft and hence was far faster than the IJAAF's current fighter, the Kawasaki Ki-10 biplane, the type was rejected by the army owing to its reduced maneuverability.

[12] Chinese Nationalist pilots, primarily flying the Curtiss Hawk III, fought against the Japanese, but the A5M was the better of almost every fighter aircraft it encountered.

Though armed with only a pair of 7.7 mm (0.303 in) machine-guns, the new fighter proved effective and damage-tolerant, with excellent manoeuvrability and robust construction.

The Mitsubishi team continued to improve the A5M, working through versions until the final A5M4, which carried an external underside drop tank to provide fuel for extended range.

US intelligence sources believed the A5M still served as Japan's primary Navy fighter, when in fact the A6M Zero had replaced it on first-line aircraft carriers and with the Tainan Kōkūtai in Taiwan.