Interesting question. I looked at the diagram shown here:
http://forum.12oclockhigh.net/attach...3&d=1295643763
I have a couple of ideas. There is an item labeled 105 "control linkage". I don't think this is the control linkage for the tail as there are other items 96 and 97 that seem to be the flight control linkages, so I think that 105 is the linkage for control of the tail gun. It is hard to track the item "forward" to see where it ends and the door seems to hide the path. So.... who might control it? I think it is "controlled" or linked to the dorsal gun. That gunner would have to have an "interrupter" on his gun to prevent him shooting off the rudder as he swings his gun from side to side as he tracks a plane approaching from the rear. I suspect that the "remote" tail gun will "follow" his dorsal gun in that narrow arc during which time "his" gun can't be fired as it would hit the rudder, but the tail gun could be fired at the rear attacking plane.
In the simplest case, the tail gun may only track the up and down movement of the dorsal gun (not side to side) and may only fire when the dorsal gun is being interrupted, i.e., when the dorsal gun is pointed back at the rudder and is trying to fire at an attacker directly behind the bomber. In this situation, to tail gun "takes over" for the dorsal gun during the time the dorsal gun can't be fired.
There seem to be two photos of two different versions of the gun on this link. Note in both cases there would not be much (if any) movement side to side but there could be some up and down movement.
http://www.4wdaction.com.au/forum/vi...502&start=3315