Doppler
It is Jun '81 and I am positioning to Akrotiri with a 70 Sqn crew. We had just crossed the Northern French coast, at around FL250, when there was a loud bang. I felt a pressure surge in my ears and the freight bay filled with water vapour mist.
I realised that we'd had a rapid depressurisation (thank you North Luffenham), climbed down from the freight stack and strapped in. The crew carried out the drills and we turned back at FL80. The Loadie told me what had happened and, together, we checked around to see if we could find the problem. There was nothing apparent, the a/c was handling satisfactorily, so we continued to LYN. On landing, we found out that the Doppler di-electric panel had failed. This was situated underneath the a/c, forward of the para doors.
As per Smudge's list, the Doppler was a British fit for the 'K'. It turned out that there had been no separate servicing inspection added for the panel, even though it formed part of the pressure hull. Of course, the panel was nowhere near as robust as the metal skin and, being underneath, was vulnerable to damage - especially during strip landings.
The whole fleet was checked and, if my memory serves, a few were changed.