The Consolidated tail turret was used on the B-24 & PBY Liberator bombers as well as the front turret on the B-24.

Consolidated tail turret completely blown out of the tail of a B-24 by a flak hit.
The manual tail turret appeared on the B-24 M model as part of an attempt to produce a lighter bomber. It had a wider turning radius than the Consolidated turret.
The Martin hydraulic tail turret was used on the PBM3D flying boat.
B-17 tail guns

Above and right: B-17G. For the B-17 G the tail position was improved and a chin turret was added under the nose.