here some words from Maarten van Delft to his photos of GYU made at a visit in 1989:

Just once in 1969 I logged the Royal Navy from Gibraltar with a vm and callsign GYU on 17468 kHz. A QSL letter confirmed my reception and the transmission had been directed to the Antarctic. On the envelope was a nice postage stamp in the characteristic shape of the Rock. About 20 years later I visited Gibraltar to obtain a QSL for my FM reception in Holland of BFBS on 99.5 MHz, as my report had not been answered.
I also visited C&W Ltd. which I had heard just once with a vm to London on 10 MHz. I was told that the HF circuit had been active briefly then during repairs of the submarine cable.
My final visit was to the Royal Navy Comcen inside the Rock. I first showed a copy of my QSL letter to a guard at HMS Rooke. (The RN have the tradition also to refer to their land bases as ships!). The guy made a phonecall to the comcen where I was welcomed a few minutes later. I first passed the pathway to the entrance. You can see on the picture that it is sheltered by concrete slabs to protect people from falling rocks. Once inside I was shown all equipment and I still remember the huge antenna switching facility. The two operators were quite friendly and at the time they were working London in RTTY on 12 MHz. You can see the signal on the monitor to the right.
They asked for my address and they later kindly sent me some booklets on Gibraltar and especially its role during WW II.