3 Top Secret Technology Demonstrator Aircraft that Could Still be Classified


Throughout the Cold War the United States and other countries spent billions of dollars developing cutting-edge military technologies in a bid to gain an edge over the opposition. Much of this work was carried out in secret at isolated locations such as the remote Nevada test site known as Groom Lake, aka Area 51. Among the ‘black projects‘ developed at Groom were high, fast flying spy planes and stealth jets, many of them one of a kind proof-of-concept aircraft.

Some of these top secret technology demonstrators have now been declassified, while others remain firmly under wraps, despite having likely been retired and potentially destroyed and buried over the years. This article features three classified aircraft that may have been built and flown over the past three decades. And while there’s no hard evidence that they were (the black project world is a murky one where misinformation abounds) there are some compelling clues.

General Dynamics Model 100 (aka Sneaky Pete)

general-dynamics-model-100-sneaky-pete (Image via Flygplan, author)

The Model 100 programme began at General Dynamics in 1976, around the time Lockheed was developing its Have Blue proof-of-concept aircraft. An early 1/4 scale Model 100 concept was known as ‘Cold Pigeon’, which evolved into a design nicknamed ‘Sneaky Pete’ by August 1977.

Originally a company-funded effort, the programme reportedly gained USAF support under the code name Have Key, and may have been developed in response to a 1983 Air Force requirement for a stealth aircraft capable of both reconnaissance and strike.

a-12-avenger-ii (Image: US Navy, public domain)

The GD Model 100 has been described as a single-seat demonstrator aircraft with a triangular planform, and is believed to have been less stealthy than Lockheed’s Have Blue or Northrop’s Tacit Blue demonstrators. It’s also thought that Sneaky Pete formed the basis of the ill-fated A-12 Avenger II (above), which was cancelled controversially in 1991 and remains a legal issue to this day. Interestingly, an ‘A-12 canopy’ appeared on eBay in 2011 (below).

a-12-avenger-canopy (Image: Seth Kettleman)

Sneaky Pete may be the source of various triangular aircraft sightings across the Antelope Valley during the 1990s. It’s also been suggested that subscale B-2 Stealth Bomber demonstrators could account for these unidentified aircraft, but there’s no solid evidence such a plane was ever built.

hangar-18-groom-lake (Image: Google Earth; Hangar 18 at Groom Lake, where Dyson’s Dock is believed to be located)

If the General Dynamics Model 100 does exist, it may be stored in a classified facility at Groom Lake (Area 51) known as Dyson’s Dock. It’s also possible it may have been buried miles from public land. What does seem certain is that, if Sneaky Pete did play a part in A-12 Avenger development, it’s unlikely to see the light of day any time soon.


Several years ago an unusual aircraft designation appeared in the official biography of test pilot Colonel Joseph Lanni. This reference – YF-24 – was later redacted, leading reporters and enthusiasts to question whether it was a classified stealth demonstrator, a foreign jet under evaluation by the USAF, or simply a typo.

Boeing-Model-24F (Image via Boeing/US Air Force study)

The Pentagon denies the existence of a YF-24. But some ‘stealth watchers’ have speculated that it could be linked to the defunct Advanced Tactical Aircraft (ATA) programme or early Joint Strike Fighter studies. The DEW Line recently posted an engineering paper for a Boeing Multirole Fighter concept that could offer a tantalising clue as to the origins of the mysterious YF-24 designation.

The design (above), known as the Model-24F, dates to the 1990s and shares common features with Boeing’s ATF concept, as well as the ill-fated X-32 technology demonstrator and future F/A-XX fighter studies.

Boeing-MRF-24X (Image via Key Publishing Aviation Forum)

While the Model-24F design apparently utilised 1998 technology, a more recent study – the MRF-24X – appears to show a tailless version of the same basic airframe. Harnessing 2003 technology, it looks to be a step closer to Boeing’s F/A-XX concept (below).

Boeing-F-A-XX (Image: Boeing via YouTube)

It’s impossible to say whether these designs reflect an evolving family of fighter demonstrators, or indeed whether such aircraft ever flew. But the similarities between their names – Model-24F, MRF-24X and YF-24 – and likeness to Boeing’s future fighter concept is nevertheless interesting.

The ‘North Sea Sighting’ – mysterious black triangle spotted in 1989

north-sea-sighting-chris-gibson (Image: Discovery Science via Disclose.tv)

In August 1989 engineer Chris Gibson, a member of the Royal Observer Corps, was working aboard the North Sea oil rig Galveston Key, when he witnessed a black, highly swept triangular aircraft. The mystery jet was accompanied by two F-111 bombers and appeared to be refueling from a KC-135 Stratotanker.

north-sea-sighting-chris-gibson-black-triangle (Image: Discovery Science via Disclose.tv)

In 2013 the aircraft’s identity remains a mystery, and explanations range from a high speed SR-71 follow-on programme to a case of mistaken identity. While there’s no hard evidence Gibson saw a classified aircraft that day, there are some tantalising clues that something’s out there.

x-15-x-24b-x-24c (Images: 1, 2, 3 NASA, public domain; X-15, X-24B & Lockheed X-24C proposal)

The so-called North Sea sighting‘s planform resembled lifting body designs of the 1970s, such as the X-24B. Interestingly, several proposals were floated between 1972 and 1978 for an X-24C – a high speed follow-on project drawing on lessons learned from the X-24B and X-15. Although the programme was cancelled, some have speculated that it continued as a black project, perhaps under a Lockheed Skunk Works contract.

b-70-valkyrie-blackstar-2 (Images: NASA, public domain; inset: Aviation Week via Wikipedia)

The mystery aircraft has also been linked to a two-stage-to-orbit system known as Blackstar, rumoured to have flown during the 1980s and ’90s, comprising a ‘mothership’ launch vehicle (similar to the XB-70 Valkyrie bomber, above) and a small spaceplane. Neither of these aircraft correspond directly to the North Sea sighting, but Aviation Week reported that an earlier technology demonstrator had proved extremely successful.


lockheed-fdl-5-mock-up (Images: USAF (via Stratosphere Models)

The aircraft’s planform also resembled a 1960s-era spaceplane concept based on the USAF’s FDL-5 design. The above photos show Lockheed’s full scale FDL-5 mockup, which some have claimed was actually a real vehicle. It’s impossible to know what to make of such claims, or whether there’s any relation between the various design studies and rumoured sightings. But it seems fair to say that Chris Gibson saw something odd in 1989 – and almost 25 years on, it remains a mystery.

Part 1 – Top Secret Technology Demonstrator Aircraft That Are Now Declassified


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