Check out this awesome combat footage in the .gif below of the WWII era B-25G Mitchell Gunship with a 75mm M4 Cannon. They were used mostly in anti-shipping campaigns. The B-25G Mitchell had two .50cal machine guns and the 75mm M4 cannon in the nose. The later B-25H had four .50cal machine guns and the 75mm M5 cannon.
Grand daddy to the A-10!