Warmtoast,
Followed your link, and got a whole feast of pics and information about the Rotor system, on the periphery of which I worked as Adj of an Auxiliary Fighter Control Unit for three early '50s years. So this was the "hole" (ours was at Seaton Snook) down which I was not permitted to go (needed a Special Clearance, you see: I'm not entitled because No Need To Know).
Our primary task was to train local girls as Radar Operators and Fighter Plotters, and our 70 trainees were every bit as glamourous as these (Note their "A"s). Thing to remember: the Plotter is more on display, but each girl's headset is linked to another's as she sits in front of a radar tube maybe fifty miles away, and she should not be forgotten as she is not protected down a hole, but at the radar towers and so liable to be (and was) often bombed.
As most people know, the system worked perfectly on the day, and was the human heart of the Fighter Command's ground control of the Battle of Britain. Now the survivors are grandmothers and great-grandmothers, I take my hat off to them.
All Warmtoast's info stirred an ancient memory: the Spitfires and (odd) Hurricane I flew in 1942 all had a circular "Remote Contactor" on the RH side of the cockpit. They were not used and we did not bother about them. On a whim I Googled <Remote Contactot aircraft WWII>
Result:
<SpitfireSpares.com - warbird Instruments> has them for sale.<Pip-squeak - Wikipedia> gives a full account. Now I know.
Danny.