My Uncle flew Cobras in the Pacifc.
My father (at 01) flew a B-25G in N. Africa for a bit. The B-25G's role was against shipping. As such, it was fitted with a big 75mm cannon in the nose. The gun was about 10 feet in length, and was loaded manually. Recoil was about two feet. He says it was pure luck if you hit anything. You see, the aiming device was a simple cross-hair bolted to the dash.
BTW: My father went on to fly a variety of fighter planes including F-84s in Korea, and F-105s in 'Nam. The man learned to fly in a bi-plane, and wound up in super-sonic jets. Quite a career.