8th AF B-17E's came equipped for 'movable' 30 cal in a ball socket on a flat plane but quickly beefed up to .50's then in the F, continued with two cheek guns enabled to fire 'nearly' forward, and then field modified a truss mounted pair in a ball joint just above the CL of the 'nose glass' - that the Bombadier could fire twin 50's staight forward - the The G model eliminated that rig with the factory turret and gunsight.
When the G came out many of the a/c commanders got rid of one or the other, or both cheek guns depending on the wishes of the bombadier and navigator - only one guy could really use the cheek gun in a spray and pray environment
Oh so cheek guns were kind of a deterent to enemy fighters attacking at those angles rather than actual accurate defensive weaponry. I always though that they would be hard to use in combat
The ball turret was safest in combat; however it the door jammed so you could not get back in the bomber (as it often did), and the landing gear failed, you would have one flat gunner.