America’s secret stealth aircraft you’ve never heard of

Alex Hollings | September 15, 2022

The United States operates more stealth aircraft than any other country on the planet, both in terms of volume and variety, with three publicly disclosed stealth platforms in service and at least three more at some stage of development.

But for every F-22 Raptor, F-35 Joint Strike Fighter, or B-2 Spirit, there are a number of stealth jets that never found their way into operational hangars — either because of program cancellations or, often, because they were never intended for combat service at all. Sometimes, these programs aim to prove advanced new technological concepts, test classified new systems, or prove the efficacy of a capability meant for inclusion in other aircraft.

Because of the very nature of the technology, new stealth aircraft are usually developed under the utmost secrecy. The F-117 Nighthawk, as one famous example, was operational for years before the American government acknowledged its existence. Likewise, prototypes, technology demonstrators, and even programs meant for service but canceled for various reasons often remain shrouded in mystery for years, even after they stop flying.

Still commonly referred to as “Black Programs,” the Pentagon has a long and illustrious history of funding the classified development of advanced technologies. Today, the most secretive efforts fall under what’s commonly referred to as Special Access Programs or SAPs, which limit the distribution of information even among those with the highest-reaching security clearances. But even within the world of SAPs, there remains another, even murkier designation: Unacknowledged SAPs, or USAPs. These efforts are so secretive that briefings are kept off paper and delivered by word of mouth only to the highest levels of government.

As we discussed recently in our in-depth coverage of the legend surrounding America’s seemingly mythical Aurora reconnaissance plane, many of these aircraft may never be revealed at all… But a few of these highly secretive stealth aircraft have managed to peek out from behind the Black Budget veil, and some may have slipped beneath your radar since their disclosure.

Related: Was America’s Aurora hypersonic aircraft real?

Boeing’s Bird of Prey

Throughout the 1990s, a team of engineers from McDonnell Douglas’ Phantom Works developed and tested a unique stealth aircraft shrowded in the secrecy of Area 51, known to most as the Bird of Prey. Unlike most stealth programs, the Bird of Prey, developed under the alias “YF-118G,” wasn’t aiming for operational service, but elements of the design and production process are still working their way into Uncle Sam’s hangars to this very day.

Perhaps the most lasting contribution this incredible and exotic airframe made to America’s defense apparatus was in its audacity and subsequent success. While most stealth aircraft are known for their high cost, the Bird of Prey went from a pad of paper to the skies over Area 51 for less than the cost of a single F-35 today. The entire program cost just $67 million from start to finish.

Powered by a single Pratt & Whitney JT15D-5C turbofan engine, which produced just 3,190 pounds of thrust, the Bird of Prey wasn’t a fighter, but it did prove that Boeing had the chops to produce a stealth aircraft while advancing technologies tied to rapid prototyping and single-piece composite material construction.

You can read more about this unusual aircraft in our full-length feature on it here.

Related: Bird of Prey: Boeing’s lost budget-busting stealth fighter

McDonnell Douglas’ A-12 Avenger II

On 13 January 1988, a joint team from McDonnell Douglas and General Dynamics was awarded a development contract for what was to become the A-12 Avenger II (not to be confused with Lockheed’s proposed A-12 of the 1960s) Once completed, the Navy’s A-12 would have been a flying-wing design reminiscent of Northrop Grumman’s B-2 Spirit or forthcoming B-21 Raider, though much smaller. The sharp triangular shape of the A-12 eventually earned it the nickname, “the flying Dorito.“

Despite clearly serving in an attack capacity, Lockheed’s F-117 Nighthawk had been given the “F” designator (and the informal moniker of “stealth fighter”) intentionally. The F-117 possessed no real air-to-air capability – a defining characteristic of a “fighter” aircraft — but Air Force officials hoped the concept of a “stealth fighter” would attract the sort of highly-skilled fighter jocks this new attack aircraft would really need.

The Navy entertained no such chicanery in their own stealth jet. It planned to saddle the platform with an “A” prefix to demonstrate its use against ground targets despite actually having the ability to engage air targets with its two internally-stored AIM-120 AMRAAM air-to-air missiles. In other words, the A-12 Avenger II would have actually been America’s first real stealth fighter.

By 1991, however, the A-12 was significantly overweight, over budget, and behind schedule, leading to its unceremonious cancellation.

You can read more about this stealth aircraft what-if in our full feature here.

Related: The A-12 Avenger II would’ve been America’s first real ‘stealth fighter

Boeing’s Model 853-21 Quiet Bird

The largely-forgotten Model 853-21 Quiet Bird is a prototype stealth aircraft that actually predates the F-117’s Have Blue precursor’s first flight by nearly a decade and a half. The effort began as a study into developing a low-observable aircraft to serve as an observation plane for the U.S. Army.

Throughout 1962 and ’63, Boeing experimented with stealth aircraft design concepts for the Quiet Bird, incorporating different shapes and construction materials in an effort to reduce the jet’s radar cross section (RCS) long before Denys Overholser at Lockheed’s Skunk Works would develop the means to accurately calculate an RCS without placing the aircraft in front of a radar array.

Although Boeing’s tests did indeed prove promising, the U.S. Army didn’t fully appreciate the value a stealth aircraft could bring to the fight and the program was ultimately shelved. However, Boeing has credited lessons learned in the development of the Quiet Bird for some of the success they would later find with the AGM-86 Air Launched Cruise Missile.

Related: Why is it so hard to develop stealth aircraft?

NASA and Boeing’s X-36 Tailless Fighter Agility Research Aircraft 

Like the Bird of Prey, the X-36 program wasn’t about fielding a new stealth aircraft for combat, so much as maturing the technologies that may eventually find their way there. Today’s stealth fighters are extremely difficult to target, but are actually not very difficult at all to spot and track using even dated radar arrays. Because of the performance requirements of a fighter, jets like the F-35 and F-22 need things like large jet inlets and vertical tail surfaces — things that can be omitted by less aerobatic stealth aircraft like the B-2 Spirit. These components don’t compromise a stealth fighter’s low-observability against high-frequency targeting arrays, but do so against low-frequency early-warning radars that aren’t capable of providing a target-grade lock.

In the mid-’90s, NASA and McDonnell Douglas (later Boeing) teamed up to try to bridge the gap between the stealth capabilities of flying-wing designs like the B-2 and aerobatic fighters like the F-22. Their X-36 was designed to fly without the empennage, or tail assembly, found on most fighters.

It was built to a 28-percent scale of a full-sized fighter, measuring just 19 feet long. It used a canard forward of the wing, split ailerons, and thrust vector control to help compensate for the missing tail. A pilot on the ground controlled the aircraft using a heads-up display connected to a nose-mounted camera.

The X-36 flew a total of 31 successful flights over just 25 weeks, racking up 15 hours and 38 minutes of flight time utilizing four different flight control software iterations.

While no subsequent aircraft has been directly linked to the X-36 program, it’s worth noting that nearly all official renders coming from the Air Force’s NGAD and the Navy’s F/A-XX fighter programs in development show stealth aircraft without conventional tail surfaces, suggesting the X-36’s legacy may simply still be shrouded in secrecy.

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