The A-prefix denoted an attack-emphasis in the A-12 design, but interestingly enough, the aircraft would have actually met the design requirements to be considered a fighter — including an onboard radar array and the ability to carry a variety of air-to-air missiles. As a result, this A-12, carrying an attack prefix, could have been the world’s first true stealth fighter, as the F-117 Nighthawk, secretly already in service, had neither onboard radar nor the ability to engage airborne targets outside the realm of hypotheticals. That’s right, the Air Force’s F-117 wasn’t really a stealth fighter, but the Navy’s A-12 actually would have been.

For some time, it seemed as though the A-12 Avenger II program was going off without a hitch, but then, seemingly without warning, it was canceled by Defense Secretary (and future Vice President of the United States) Dick Cheney in January of 1991. It was only later revealed that the A-12 Avenger II was significantly overweight, over budget, and behind schedule.

Despite a number of other efforts over the years, it would ultimately take 26 more years for the U.S. Navy to get a stealth fighter onto the decks of its carriers in the F-35C.

You can read our full feature on the A-12 Avenger II’s development here.

BOEING 747 CMCA: THE MOST COST-EFFECTIVE BOMBER CONCEPT IN U.S. HISTORY

During the 1960s, the United States began fielding intercontinental ballistic missiles (ICBMs) in land-based silos, as well as submarine-launched ballistic missiles (SLBMs) carried by stealthy sub-platforms strategically positioned around the globe. With America’s defense posture primarily oriented toward deterring Soviet aggression, these new methods of delivering nuclear payloads prompted many within the public and politics, to question the need for expensive new bomber development programs. By 1977, this pervasive line of thought took root in the Carter administration, leading to the cancelation of the supersonic heavy payload B-1 bomber effort.

Boeing, recognizing that this cancelation could leave a gap in America’s strategic capabilities, set to work developing an extremely cost-effective bomber-of-sorts to meet this need at a much lower price point. The firm ultimately settled on plans to load a 747 with as many as 72 AGM-86 air-launched cruise missiles carried in nine internal rotary launchers, allowing this commercial people-carrier to serve instead as a long-range arsenal ship capable of wiping out targets from hundreds of miles away. This design, dubbed the 747 Cruise Missile Carrier Aircraft (CMCA), may sound crazy… but it was actually extremely practical in a number of important ways.

With an unrefueled range of 6,000 miles, the ability carry to 77,000 pounds of ordnance, and pre-existing global infrastructure already established for the 747 line, this CMCA concept would have produced the most cost-effective bombing platform in modern history. Today, the B-52 Stratofortress costs approximately $88,000 per flight hour, the B-2 Spirit rings in around $150,000 per hour, and the B-1B Lancer burns through around $173,000 per hour.

The 747 on the other hand, costs just $30,950 per hour to fly, all while carrying a larger payload than any of America’s in-service bombers.

Ultimately, the 747 CMCA never made it off the drawing board, however, with the Reagan administration pulling the B-1 program out of mothballs and the B-2 entering service shortly thereafter – but we may see the U.S. revisit a similar concept in the future. After all, there are already a number of commercial airliners filling other military roles today, from the Boeing 707-based KC-135 to the 747-based E-4B National Airborne Operations Center.

CONVAIR NB-36: DELIVERING NUCLEAR PAYLOADS WITH NUCLEAR-POWERED BOMBERS

The NB-36 Crusader was an experimental nuclear-powered bomber that actually flew with a nuclear reactor onboard during testing.

The NB-36 was based directly on the absolutely massive Convair B-36 Peacemaker. With a 230-foot wingspan, the B-36 still holds the title for the longest wingspan of any combat-coded aircraft. Its wingspan was so big, in fact, that you could lay a B-52 Stratofortress’ wings over the B-36’s and still have room to throw a Super Hornet on the end for good measure. Thanks to its massive size, the B-36 could fly with an 86,000-pound payload onboard — and in the 1950s, the Air Force experimented with using some of that payload capability to equip the bomber with its own nuclear powerplant — allowing it to fly almost indefinitely like a nuclear-submarine in the sky.

The NB-36 that resulted carried a one-megawatt, air-cooled nuclear reactor that hung on a hook inside its cavernous weapons bay. This reactor then had to be lowered through the bomb bay doors into shielded underground facilities for storage between flights. In theory, a nuclear-powered bomber could stay airborne for weeks at a time (if not longer) and could reach any target on the planet without the need to land or refuel.

At the time, the United States maintained a state of constant readiness in its nuclear-armed bomber fleets to serve as a potent deterrent against Soviet aggression. This policy would later mature in Operation Chrome Dome — an effort that resulted in the U.S. having airborne B-52s armed with nuclear weapons 24 hours a day for eight straight years. As you might imagine, this policy was rather expensive… but it’d get a whole lot cheaper if Uncle Sam didn’t have to pay for fuel.

Rather than using jet fuel, the NB-35’s nuclear reactor would power four GE J47 nuclear-converted piston engines, each generating 3,800 hp, which were then augmented by four additional turbojet engines that produced 5,200 lbs of thrust. The HTRE-3 was a direct-cycle system that pulled air into the compressor of the turbojet and through a plenum and intake that led to the core of the reactor where the air served as coolant. From there, the super-heated air would travel into another plenum that led to the turbine section of the engine before exiting as exhaust out the back.

But despite the effort’s promise, the risks associated with flying a nuclear reactor over American or allied airspace ultimately led it its cancellation in 1961.

LOCKHEED X-24C: A SCRAMJET-POWERED HYPERSONIC AIRCRAFT IN THE 1960S

The X-24C was part of an effort to field a scramjet-powered hypersonic research aircraft beginning in the late 1960s. Taking on the role of lead contractor, Lockheed worked side by side with the Air Force’s National Hypersonic Flight Research Facility and NASA to develop and field two hypersonic test aircraft, with each vehicle slated for 100 flights.

The decision was made to equip this new “L-301” program’s aircraft, unofficially dubbed the X-24C, with a new LR-105 rocket engine found at the time in the Atlas series of rockets. The LR-105 would launch and accelerate the X-24C to hypersonic speeds, not unlike the rocket engine that powered the X-15. From there, a second hydrogen-fueled, air-breathing scramjet (supersonic-combustion ramjet) engine mounted on its belly would fire up and take over.

The scramjet engine would propel the X-24C to sustained speeds in excess of Mach 6, reaching intended peak speeds that were higher than Mach 8, or more than 6,130 miles per hour. The aircraft itself resembled the lifting body design leveraged by the Martin Marietta X-24A and B programs that tested unpowered reentry flight characteristics.

In a real way, the L-301 program and its X-24C could be seen as the precursor to ongoing legends about Lockheed Martin’s combined cycle turbofan/scramjet SR-72, the Air Force Research Laboratory’s Mayhem program, and even Hermeus’ combined cycle turbofan/ramjet hypersonic aircraft efforts. Had the X-24C program continued, it would have given the U.S. a scramjet-powered hypersonic aircraft in the 1960s. Instead, the U.S. now appears to still be years away from fielding a reusable, airbreathing aircraft for testing, let alone service.

But by the end of 1977, however, the L-301 program and its notional X-24C were canceled in favor of a different Lockheed developmental effort that would change the value proposition associated with sheer speed. That effort, of course, was Have Blue, which later matured into the F-117 Nighthawk.

Alex Hollings is a writer, dad, and Marine veteran.

This article was first published by Sandboxx News.

Image: Shutterstock