AA cannon

An autocannon or automatic cannon is a large, fully automatic, rapid-fire projectile weapon that fires armour-piercing and/or explosive shells, as opposed to the bullet fired by a machine gun. Autocannons have a longer range and a larger calibre than machine guns (e.g., 20 mm or greater, most often in the range of 20–57mm, but bigger also exist), but are usually smaller than tank guns, howitzers, field guns or other artillery. When used on its own, the word "autocannon" indicates a non-rotary weapon. When multiple rotating barrels are involved, the word "rotary" is added, and such a weapon is referred to as a "rotary autocannon" https://en.wikipedia.org/wiki/Autocannon