A thru F models had actual Tail gunners. G’ and H models had gunners up front.
Also around the time of the Gulf War the guns were removed from all the BUFF’s as with new fighters and missile technology they did not have to get close to use guns to down one anymore...
I believe the gunner position because the defensive systems operator and controlled radar/IR jammers, countermeasures, and watched the radar for any planes or missiles.
When in Air Force tech school, (Crew Chief) the instructors told us that a few times in Viet Nam when the aircraft was hit, and communications was lost between the tail gunner and the rest of the crew, the tail gunner would bail out, not knowing that the thing was still air worthy. So the aircraft would return to base with no tail cone, and no tail gunner.
I can't verify that story, but they wouldn't lie to me , would they?