The Douglas SBD Dauntless's rear gunner could shoot its own tail.
The SBD-5 had two 30-cal machine guns that could be popped out of storage in the aft fuselage and locked into a ring frame around the gunner's seat. That seat can rotate and pivot in several directions. The gun is mounted on a ball joint that allows it to rotate freely.
There is no mechanism or stop to prevent the gunner from shooting off the vertical tail. It might have been impossible to shoot off the horizontal tail, but I don't quite recall.
I used to volunteer for an organization that restored, maintained, and flew an SBD-5 as a flying museum. I've spent several hours in the back seat on pleasure flights, cross countries to airshows, and flying in airshows and photo flights. This is me in the back seat.
One year, we hosted a reunion for a SBD squadron. Seeing those old timers interact with their airplane again was amazing. I remember one 80+ year old who hobbled with a cane. His face lit up when we said he could touch the airplane and even more so when we said he could get in. We prepared to help/lift this guy into the back seat when he dropped his cane and with one swift motion was up the side and into the back seat. Before you know it, he had the seat turned around and the guns drawn. It was all one fluid motion of 60+ year old muscle memory. It was beautiful and heartwarming.
A woman asked him "What kept you from shooting the tail off?". He gave the deadpan response "Fear of dying."