Elsewhere, I also know that Dr Clarke was interviewing a former high-level defence source when the latter, unprompted, turned the conversation to Calvine and said:
that the diamond was real,
that it was American,
that it had been tested over the low countries (presumably playing a part in the 1989-1991 UFO flap),
that it was used in the Gulf War,
and that its defining purpose had been to loiter over enemy territory and scan for targets to be subsequently destroyed by B-2 stealth bombers.
If anyone is also able to privately share a copy of the PhD thesis, Ehrhard, Thomas, "Unmanned aerial vehicles in the United States armed services: A comparative study of weapon system innovation", I'd be grateful to hear from them, too.
Thank you.
The aircraft you are describing was the QUARTZ/AARS UAV, during the period where Lockheed was prime contractor and the program was an intelligence agency project.
It was a large flying wing, similar in shape to the X-56.
It was (supposedly) able to fly at very low air speeds, below 100 mph. From the ground it would appear to be barely moving or stationary.
The center body / fuselage was faceted, and from some angles may have looked vaguely like a diamond.
It was not used in the Gulf War. In the late 1980s a prototype or demonstrator crashed, resulting in a redesign and restructuring of the program and greater USAF participation as well as Lockheed partnering with Boeing. During the Gulf War it is very unlikely that anything related to this program was flying.
During the 1990s there were rumors that American classified aircraft were tested / flown in the UK. I tried through the late 1990s and early 2000s to find anything to substantiate that. I never found anything at all to substantiate it. It seems very very unlikely that any US classified aircraft was tested over the UK. There was no compelling reason to. The inverse, however, probably did happen (UK aircraft tested in the US).
The diamond pictured in the photograph does not correspond to any classified aircraft or research in the US that I am aware of.