Here's What You Need to Know: A few of these planes are still around, mothballed in a hanger somewhere.

In the 1950s and ‘60s, American plane-makers went crazy developing new fighters, bombers and reconnaissance aircraft for the U.S. armed services. Some of the most successful designs -- the F-4, the F-15, and B-52 -- remain in service today.

Other concepts failed. Some of them, spectacularly. Here are a few.

Convair YB-60

In the early 1950s, the U.S. Air Force wanted a turbojet-powered heavy strategic bomber to lug atomic bombs across oceans. Convair had built the piston-engine B-36 for the Air Force and decided that simply swapping out the B-36’s prop motors for jets — among other modest changes — would suffice to produce a winning new bomber.

The result was the YB-60, a 171-foot-long monster of a warplane sporting eight J57 turbojets. The first of two prototypes took off on its inaugural flight in April 1952. The YB-60 could fly 2,900 miles at a cruising speed of 467 miles per hour while lugging a 36 tons of bombs.

Impressive, sure — but not as impressive as the performance of the YB-60’s most direct competitor, Boeing’s B-52. The eight-engine B-52 cruises at 525 miles per hour over a distance of 4,500 miles while carrying 35 tons of bombs.

The Air Force cancelled the YB-60’s test program in January 1953. B-52s remain in the U.S. inventory.

Bell XF-109

In 1955, the U.S. Navy and Air Force approached Bell Aircraft Corporation with a far-out idea — design a Mach-two fighter capable of launching and landing vertically. Bell dutifully drew up a design for what it unofficially called the XF-109.

Fifty-nine feet long, the XF-109 featured a startling eight J85 jet engines — four afterburning motors arranged two apiece in rotating wingtip nacelles, plus another two afterburners in the rear fuselage and a pair of non-afterburning J85s pointing downward behind the cockpit.

With distinct rearward- and downward-blasting powerplants, the XF-109’s basic form is not dissimilar to that of the F-35B supersonic jump jet that Lockheed Martin designed for the U.S. Marine Corps 40 years later.

But the XF-109 was clearly ahead of its time. The Navy and Air Force both lost interest and the military cancelled the Bell jump jet in 1961 before the company could build any actual prototypes. The Harrier, the world’s first operational vertical-takeoff-and-landing fighter, flew for the first time in 1967. The Harrier is subsonic.

Lockheed RB-12

In January 1961, Lockheed’s legendary airplane-designer Kelly Johnson delivered an unsolicited proposal to the U.S. Air Force. His idea was to take the Mach-3 A-12 spy plane — the predecessor of the iconic SR-71 Blackbird — that Kelly had designed for the CIA and modify it into a very fast strategic bomber. More or less in parallel, Johnson was working on a missile-armed F-12 fighter version of the A-12. 

The Air Force liked the RB-12 Mach-3 bomber idea but counter-proposed with a slightly altered design it called the RS-12. Take the A-12’s sled-like titanium airframe with its powerful J58 turbojets. Add a sophisticated, long-range radar and a nuclear-tipped air-to-ground missile based on the AIM-47 air-to-air missile that also armed the F-12.

The plan was for the RS-12 to penetrate Soviet air space at Mach 3.2 and 80,000 feet and fire a single missile from 50 miles away, striking within 50 feet of its aimpoint within a Soviet city.

The Defense Department ultimately canceled the F-12 on cost grounds and opted not to proceed with the RS-12, as ballistic missiles were beginning to supplant manned bombers. The Air Force did ultimately acquire the SR-71 reconnaissance version of the A-12 and operated it into the 1990s.

Convair Model 49

In the 1960s the U.S. Army was growing sick of its long dependence on inappropriate U.S. Air Force planes for close-support missions. Aircraft such as the Republic F-105 were simply too fast and too vulnerable to support troops on the ground effectively.

Instead, the Army wanted the versatility and forward-basing possibilities of a vertical-takeoff platform that could also hover. To excel in the tough close-support role, the type would need to be heavily armed and armored. This need led to the Advanced Aerial Fire Support System program.

Convair, a company famed for its adventurous designs, responded to the Army’s AAFSS requirement with typical ambition. Drawing on its experience with the tail-sitting XFY-1, the company proposed a two-man ring- or annular-wing ducted-fan design quite unlike anything else in service, though somewhat similar to French firm SNECMA’s experimental C.540.

The concept was bizarre in appearance, but Convair believed it was the perfect configuration for an aircraft combining a helicopter’s unusual abilities with some of the offensive features of a military ground vehicle.

One of the greatest challenges was creating a cockpit that tilted so the pilot was not facing the sky in the take-off and landing and ground-based modes. This necessitated a complex, hinged forward fuselage, giving the type its distinctly Transformer-like looks.

Lockheed CL-1200

In the late 1960s, Lockheed saw an opportunity. Anticipating worldwide demand for 7,500 advanced but — in the company’s own words — “reasonably-priced” jet fighters over the next decade, in 1971 it began circulating a proposal for an improved, safer CL-1200 Lancer version of the speedy but notoriously hard-to-fly F-104.

Lockheed’s Skunk Works division, with famed designer Kelly Johnson still in charge, enlarged the F-104’s wing and fin, shifted the tailplane lower on the fuselage, tweaked the engine inlet, added internal fuel capacity and replaced the F-104’s J79 engine with a TF33. The resulting CL-1200 was, in theory, more maneuverable and controllable than the F-104 and cost around $2 million per copy, assuming a large production run. At the time, a new F-4E cost at least $2.4 million.

Lockheed entered the CL-1200 into the U.S. military’s International Fighter Aircraft competition, which aimed to select an export warplane for America’s allies. But Northrop’s F-5E won the contest, and Lockheed scrapped the CL-1200 concept, having only ever produced a mock-up of the plane.

David Axe served as Defense Editor of the National Interest. He is the author of the graphic novels War Fix, War Is Boring and Machete Squad.

This article first appeared in 2019.

Image: Wikimedia Commons