A report in _Aviation Week and Space Technology_ in mid 1991 described a
"triangular flying wing" reconnaissance aircraft, developed by Northrop
(now Northrop Grumman) from 1982, designated TR-3A and nicknamed "Black
Manta".  According to the report, the aircraft had a length of about 13
metres, wingspan of about 19 metres, and a range of 5600 kilometres; it had
been deployed for trials to Alaska, Okinawa, Panama, and the UK, and a few
had been employed in Desert Storm in the reconnaissance role.  The aircraft
was apparently developed from a Northrop technology demonstrator known as
THAP (Tactical High Altitude Penetrator), which first flew in 1981 and was
similar in design, but slightly smaller.  After this report, however,
nothing more was heard of the TR-3 for two years.

In 1993, Steve Douglass, an amateur "stealth watcher" who keeps an eye on
the USAF's "black" programmes for a hobby, took a videotape of an aircraft
landing at White Sands Missile Range.  Enhancement of the image revealed a
formerly unknown aircraft, almost certainly the TR-3.  Apart from having a
curved trailing edge, it resembled a scaled-down B-2 (or a Horten IX; see
section E.1).  It appears to be a single-seat, twin-engine, approximately
triangular flying wing, which fits the description given in the earlier
report.  You can find more details, including an artist's impression based
on the video images, in the February 1994 issue of _Wired_.

Of the various "black" aircraft supposed to be flown by the USAF (see also
section C.2), more solid evidence exists for the TR-3 than any other, and
its existence seems virtually certain.  Although it's difficult to judge
the exact size of the aircraft from Douglass's image, the dimensions quoted
in the original report are plausible.