Guns

Nearly every aircraft carries guns, and in the propeller era they are the only weapon there is. The instruments show machine-gun ammunition as MG and cannon ammunition as CNN. Both fire together when guns are selected.

Machine guns and cannon

Machine guns fire fast but do little damage with each round.
Cannon fire slower, heavier rounds that hit far harder. They are the only guns that can pierce a U-boat’s pressure hull.
Some bombers carry gun turrets that aim and fire by themselves. Press T to toggle them.

Aiming

Guns fire straight ahead, and their rounds take time to arrive. Aim ahead of a moving target, at the lead indicator.
Rounds that travel past their range are gone, so open fire only when the lead indicator appears.
Lower-level aircraft can’t aim their guns far from where the nose points.

Reloading

Guns reload by themselves when they run dry. Press R to reload early. Land on a friendly aircraft carrier to rearm at once.

Reading a plane’s page

A gun is listed like this: 4 × 20mm cannon (195r 12r/s 800m 705m/s 10s) [540dps total]. That is four 20mm cannon, each holding 195 rounds and firing 12 rounds per second, with a range of 800 meters and a muzzle velocity of 705 meters per second. They reload in 10 seconds, and together deal 540 damage per second.