In September 1969, three Lockheed engineers put their names to a report with a dry title: A Study of Very Large Nuclear-Powered Aircraft in a Potential Mission Application. Inside was one of the largest flying machines ever drawn. Its wings would have spanned 340 metres, more than three football pitches end to end, and it would have weighed well over 5,000 tonnes at take-off. A nuclear reactor would have kept it in the air for weeks.

The design is now known as the Lockheed CL-1201, and it has become a favourite of social media as the “nuclear flying aircraft carrier”. That is one version of it. The full story is stranger, and in places less certain, than the viral posts suggest.

Fifteen Times a Jumbo Jet

The best record of the design is not a glossy brochure but a 1971 NASA technical report on nuclear-powered transport aircraft by Frank Rom and Charles Masser of NASA’s Lewis Research Center. They reprinted Lockheed’s three-view drawing and its specifications as an example of how far large aircraft studies had gone.

The numbers in that drawing are staggering: a crescent-shaped wing 340 metres across with an area of 11,630 square metres, a fuselage 170.7 metres long, a height of 46.6 metres and a gross weight given as 5,375 metric tons (the figure caption rounds it to 5,450). NASA noted that the aircraft could carry about 40 percent of its weight as payload, and that its structure, made from conventional materials, was a normal 25 to 30 percent of gross weight. In other words, the engineers did not think the size alone made it impossible.

A Reactor Instead of Fuel Tanks

For cruise, the aircraft would have used turbofan engines heated by a nuclear reactor rather than by burning fuel. In the reactor concept NASA described, a compact, helium-cooled reactor heats gas that is piped to heat exchangers in the engines, so they could run on nuclear heat in cruise or on ordinary fuel when needed. Lockheed’s drawing, shown at the top of this article, has four of these engines at the rear.

A reactor cannot deliver the bursts of thrust needed to lift more than 5,000 tonnes off the ground, so the design added chemically fuelled lift engines in the wings and nose. Later accounts put their number for the carrier version at 182. NASA even suggested replacing the wheels with an air-cushion landing gear, which would have let the aircraft operate from rough ground or water.

Safety was central to NASA’s analysis. Its reactor was wrapped in a containment vessel built to survive a crash at up to 305 metres per second, and the shielding was sized so that the radiation dose 9 metres from the reactor would be lower than the cosmic radiation a passenger receives at 35,000 feet.

The Flying Aircraft Carrier

Lockheed’s study looked at more than one mission. One version was a logistics transport, carrying troops and cargo around the world without refuelling. The version that has captured the imagination was an airborne aircraft carrier, a mothership that would cruise for weeks with fighters slung under its wings, launching them where they were needed and taking them back on board.

Here the record becomes thin. The detailed figures for the carrier come from secondary sources, chiefly the aviation writer Bill Gunston, and they do not agree. The number of fighters is given as 22 or 24. The crew is given as 845 in one account and anything from 400 upward in others. The endurance of about 41 days is an estimate, and the original basis for it is not documented. No surviving source explains in detail how the fighters would have been launched and recovered in flight.

The idea itself was not new. In the early 1930s the US Navy flew two real flying aircraft carriers, the airships USS Akron and USS Macon, which launched and recovered small Curtiss F9C Sparrowhawk fighters on a trapeze lowered from their hangars. Both airships were lost in accidents, and the concept died with them.

America Had Already Flown a Reactor

A nuclear-powered aircraft was not pure fantasy in 1969. Between 1955 and 1957 the US Air Force flew the Convair NB-36H, a modified B-36 bomber that carried a working nuclear reactor on 47 flights. The reactor did not power the aircraft; it was there to test shielding and the effects of radiation on the crew and equipment. The whole Aircraft Nuclear Propulsion programme was cancelled by President Kennedy in March 1961 after about 15 years and roughly a billion dollars.

Why It Never Flew

There is no record of a formal decision to cancel the CL-1201. It was a paper study, and as far as published sources show, the Department of Defense kept no record of what became of it. The usual explanations, enormous cost, the size of the target it would present and the political impossibility of flying reactors over populated areas, are reasonable, but they are commentators’ explanations rather than documented reasons.

What the Viral Posts Get Right and Wrong

The Instagram posts circulating about the CL-1201 get the outline right: a late-1960s Lockheed study, a nuclear reactor heating the air for four large engines, an endurance of weeks and a carrier version that would have carried fighters. They leave out the 182 chemical lift engines it would have needed to get off the ground. The “22 fighters in pylons and bays beneath its wings” is one of two disputed figures, and no source describes bays for them. And the claim that “structural hurdles” killed it runs against NASA’s own assessment that the structure was of normal proportions for an aircraft.

Sources: NASA Technical Memorandum X-2386, F. E. Rom and C. C. Masser (NASA Lewis Research Center, November 1971), citing G. D. Brewer, S. Dalton and P. J. Sibley, Lockheed report LR-22802 (12 September 1969); Secret Projects forum (citing Bill Gunston); Wikipedia, Lockheed CL-1201 and Convair NB-36H; US Comptroller General report on the Aircraft Nuclear Propulsion Program (1963); Richard K. Smith on the Akron and Macon airships