Preface – Except for a few F4U’s arriving at Henderson Field in late 1942, and a very few P-38’s [whose first combat action was Dec 27th that year] it wasn’t until mid 1943 when F6F Hellcat fighters became operational for the Navy that we finally obtained the upper hand. Prior to that time it was the under-powered and limited ranged F4F Wildcats holding the line against the highly maneuverable “Zekes”, our call sign for the Zero. The USAAF had obsolescent P-40’s and P-39’s; the former, while almost equal to the Zero in speed, did not dare try to dogfight with them. The lesser known P-39, a mid engined fighter with a 37mm cannon firing thru the propeller hub, was of mediocre performance, and was also easy prey.
Performance of these planes deteriorated at higher altitudes and they had a poor rate of climb. Their brave pilots employed hit and run tactics, using speed and firepower to get away, or become the Zero’s victims.
From Wikipedia; I kept only essential links:
The Mitsubishi A6M “Zero” is a long-range fighter aircraft manufactured by Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and operated by the Imperial Japanese Navy from 1940 to 1945. The A6M was designated as the Mitsubishi Navy Type 0 carrier fighter (零式艦上戦闘機 rei-shiki-kanjō-sentōki), or the Mitsubishi A6M Rei-sen. The A6M was usually referred to by its pilots as the “Reisen” (zero fighter), “0” being the last digit of the imperial year 2600 (1940) when it entered service with the Imperial Navy. The official Allied reporting name was “Zeke“, although the use of the name “Zero” was later adopted by the Allies as well.
The Zero was considered the most capable carrier-based fighter in the world when it was introduced early in World War II, combining excellent maneuverability and very long range. The Imperial Japanese Navy Air Service (IJNAS) also frequently used it as a land-based fighter.
In early combat operations, the Zero gained a legendary reputation as a dogfighter, achieving an outstanding kill ratio of 12 to 1, but by mid-1942 a combination of new tactics and the introduction of better equipment enabled Allied pilots to engage the Zero on generally equal terms. By 1943, the Zero became less effective against newer Allied fighters because of inherent design weaknesses and the failure to develop more powerful aircraft engines. The Allied fighters gained greater firepower, armor, and speed, and approached the Zero’s maneuverability, and the Mitsubishi A6M was outdated by 1944. However, the Zero continued to serve in a front line role until the end of the war because design delays, and production difficulties, hampered the introduction of newer Japanese aircraft. The Zero was also adapted for use in kamikaze operations during the final year of the war in the Pacific. Japan produced more Zeros than any other model of combat aircraft during the course of the war.
By Unknown – Japanese Naval Aces and Fighter Units of WWII, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4445990