It isn't a turret as such but it was a hatch that allowed access to this special equipment which I have removed from the diagram otherwise it would have been a giveaway.
Technical problems here. I may be slow to respond, broadband dropped out earlier today. It is back, it used to be 4.2 mps then we had a new telephone cable it dropped to 1.8 mps now it is worse than dial up at 17 kps:argh::argh::argh: