Must land with friendly infantry. Upgrades artillery, air superiority combat or strafe
Generic prewar biplane fighter
Fighters are the most well-rounded unit in the game. Their high attack and defense strength makes them very powerful as well. However, they are very expensive.
Fighters can scramble to nearby strategic bombing raids (SBRs), amphibious assaults, and sea battles. This can only be done from an airbase, and to neighboring territories/sea zones only, and the fighters cannot do any other moves/combat that turn. This is useful for defending important areas, but it can only be done from territories which have an airbase.
Fighters can be carried on carriers. When carriers go into sea combat, the fighters enter as well (if they are your fighters, friendly fighters are just cargo). Fighters can also "launch' from carriers and enter combat in other territories/ sea zones and land back at the carrier or in friendly territory. This makes carriers very powerful, effectively mobile airbases.
Fighters can escort and intercept bombers. When escorting, they enter the SBR and attack enemy interceptors. When intercepting, they attack the incoming enemy aircraft. This makes for some exciting air battles which do not involve land units.
Appearance changes to a jet fighter (either a late WW2 concept or an early cold war fighter).