Fairchild Republic A-10 Thunderbolt II
While the A-10 has a lot of room on its wings to carry bombs and missiles, its main weapon is the front mounted gun, called the GAU-8 Avenger.  It is a very long and heavy gun called a Gatling cannon, since it is a both an autocannon (fires large bullets very fast) and Gatling gun (has more than one barrel, which spins while shooting).  The Avenger is so big that the A-10 had to be designed around it, leading to a joke that the A-10 does not have a gun attached, but the Avenger has a plane attached. The A-10 is the only aircraft to use the Avenger. Other American planes use the smaller Vulcan, also a Gatling cannon that uses smaller bullets.