Since the very inception of manned flight, the United States has invested heavily in fielding game-changing military aircraft that leverage cutting-edge technology to provide a tactical or strategic edge over the nation’s peers or competitors. This drive to dominate the skies over the battlefield led the U.S. to field the world’s first military aircraft in 1908, the first aircraft to break the sound barrier in 1947, the world’s first supersonic bomber in 1960, the world’s first manned hypersonic aircraft in 1967, and of course, the world’s first stealth aircraft in 1983… just to name a few prominent blips on the U.S. military aviation timeline.

But for every F-117 that makes it into service, there’s a long list of aviation programs that never quite made it. Sometimes, these efforts leaned too hard into the cutting edge, resulting in capable aircraft that were just too expensive to field in real numbers. Other times, these efforts were built around misconceptions about aviation that, in the days before computer simulations, could only be proven wrong through trial and error.

The existential threats that fueled military procurements throughout the Cold War led to a renaissance in aviation technology. Programs that would never see funding under normal circumstances were suddenly seen as worthwhile ventures in the name of securing any kind of advantage in the nuclear hellfire of a Third World War that, at the time, seemed inevitable to many in power.

Yet, even the massive military expenditures of the Cold War could only fund so many technological revolutions. And some platforms or programs that could have very changed the way mankind perceived airpower were just too expensive, too far-fetched, or too ahead of their time to secure their share of the Pentagon’s coffers, dooming these prototypes, concepts, and X-planes to the secretive confines of America’s sprawling library of military what-ifs.

Here are some of these game-changing programs that never got their chance to actually change the game.

BOEING X-20 DYNA-SOAR: A HYPERSONIC SPACE BOMBER THAT PREDATES SPUTNIK

Born out of Germany’s World War II efforts to create a bomber that could attack New York and continue on to the Pacific, Boeing’s X-20 Dyna-Soar was to be a single-seat craft boosted into the sky atop American rockets. That’s right, in the 1950s, the Dyna-Soar would have been the world’s first hypersonic bomber. In fact, the Dyna-Soar was very similar in both concept and intended execution to China’s fractional orbital bombardment system that drew headlines the world over after a successful test in 2021, despite the X-20 program pre-dating the launch of Sputnik 1. So… it’s safe to say this effort was a fair bit ahead of its time.

After launch, the X-20 would soar along the blurred line between Earth’s atmosphere and the vacuum of space, bouncing along the heavens by using a lifting-body design and hypersonic speeds to skip along the upper reaches of the atmosphere. It would circle the globe, releasing its payload over Soviet targets miles below, before making its way back to American territory to come in for a gliding landing, not entirely unlike the Space Shuttle decades later. The X-20 was a 1950s science fiction fever dream born of the nuclear age and the earliest days of the Cold War… and according to experts at the time, it very likely would have worked.

By 1960, the spaceplane’s overall design was largely settled, leveraging a delta-wing shape and small winglets for control in place of a traditional tail. In order to manage the incredible heat of re-entry, the X-20 would use super alloys like the heat-resistant René 41 in its frame, with molybdenum, graphite, and zirconia rods all used for heat shielding on the underside of the craft.

The program was so promising, in fact, that in that same year, the Pentagon tapped a group of elite service personnel to crew this sub-orbital hypersonic bomber. Among them was a 30-year-old Navy test pilot and aeronautical engineer named Neil Armstrong, who would go on to leave the program two years later for even greater heights as a part of NASA’s Gemini and Apollo missions.

Armstrong’s departure was a sign of things to come. After the launch of Sputnik in 1957, the United States saw a pressing need to focus its resources toward orbit itself, canceling this sub-orbital bomber effort to reallocate funds toward new space ventures within America’s fledgling space-fairing organization, NASA.

BOEING QUIET BIRD: A STEALTH JET THAT PREDATES THE F-117 BY DECADES

On December 1, 1977, Lockheed’s Have Blue technology demonstrator took flight for the first time, making a significant leap toward fielding the aircraft’s successor, the F-117 Nighthawk, just a few years later. But more than a decade and a half before Have Blue saw a runway, Boeing’s largely-forgotten Model 853-21 Quiet Bird was already making significant strides toward being the world’s first operational stealth aircraft.

While various aircraft have laid dubious claims about being the first to field “stealth” because of design or material happenstance (we’re looking at you, Ho 229), the Quiet Bird effort actually was aimed at 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 a design’s radar return without actually building it to stick in front of a radar array. In effect, the Quiet Bird’s stealth development was a very expensive game of guess-and-check.

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. If the Army had been more forward-thinking, the Quiet Bird may have offered a low-observable battlefield reconnaissance platform by the late 1960s, kickstarting the stealth revolution more than a decade earlier and almost certainly changing the way airpower has matured in the decades since.

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.

CONVAIR KINGFISH: THE HIGH-FLYING ALTERNATIVE TO THE BLACKBIRD

When Lockheed’s U-2 spy plane entered service, Soviet air defenses were already capable of tracking the high-flying platform. American officials knew it was only a matter of time before tracking the Dragon Lady turned into targeting it, so, the CIA tasked both Convair and Lockheed with developing a new reconnaissance platform that could fly at higher altitudes, at significantly faster speeds, and have a reduced radar cross-section to minimize the chances of being shot down.

Lockheed would ultimately meet these requirements in their A-12 and subsequent SR-71, but Convair’s Kingfish was its primary competitor until then. Today, Convair’s Kingfish offers us an interesting glimpse into what could have been, if not for the unrelenting genius and budget-mindedness of Lockheed’s Kelly Johnson.

The Kingfish developed out of what remained of Convair’s first attempt, known as the First Invisible Super Hustler or FISH. The FISH would have been carried aloft by a modified B-58 Hustler before being launched and powered by onboard ramjets to speeds in excess of Mach 4. But with concerns about the complexity and cost of the FISH concept, Convair was instructed to go back to the drawing board to come up with a new design built around the Pratt & Whitney J58 “turboramjet” — the same propulsion system Lockheed was working with in their A-12 design proposal.

The resulting Kingfish design was rather forward-leaning for its time, tucking its two J58s deep inside the aircraft’s angular fuselage to limit the radar return they could produce. Its delta-wing design bore a striking resemblance to the stealth aircraft that would follow decades later, but it was that emphasis on stealth that may have ultimately done the Kingfish in.

Pentagon officials, spurred in no small part by criticisms from Lockheed’s legendary Kelly Johnson, feared the Kingfish incorporated too many untested technologies to be built, tested, and operated within the program’s assigned budget. Johnson was outspoken in his views that the Kingfish design compromised performance in favor of stealth — something that was seen as a mistake at the time, despite becoming commonplace in the stealth platforms of today.

Ultimately, Lockheed’s proposal won the day, and the Kingfish was relegated to the what-if file.

MCDONNELL DOUGLAS/GENERAL DYNAMICS A-12 AVENGER II: A CARRIER-CAPABLE STEALTH FIGHTER IN THE 1980S

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, which led to the SR-71. Once completed, this Navy 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 and with harder angles.

Although the A-12 Avenger II utilized a flying wing design, its overall shape differed from the triangular B-2 Spirit under development at the time for the Air Force. The sharp triangular shape of the A-12 eventually earned it the nickname, “the flying Dorito.“