Black triangles were reported some ten? or so years ago in the
countryside around Southport, Merseyside. I think the reports
were of them rotating, close to the ground. I think the sightings
were spread over a period of weeks but my memory of the details
isn't great.
Many people saw them, including a member of my own family and
a photograph appeared on the front of the local paper,
the Southport Visiter (sic - they do spell it like that!).
I have always assumed that the closeness of these shapes to
the Stealth Bomber made it more or less certain that they were
the Stealth Bomber, at a time when it was less widely discussed.
But then UFOs have always mimicked the technology of the time
and I love the mysterious tales of airships, from, er just before
the time when there were airships.