Overview
The Hindenburg caught fire while mooring at Lakehurst, New Jersey, on the evening of 6 May 1937. The claim is that it did not catch fire on its own — that a bomb was placed aboard, most often by someone acting against the Nazi regime, and that the finding of an accidental ignition was a diplomatic convenience.
Two things about the disaster are worth stating before anything else, because both are routinely lost.
The first is the survival rate. Ninety-seven people were aboard. Sixty-two of them lived. Thirty-five died on the airship and one member of the ground crew was killed, thirty-six in all. The footage suggests nobody could have walked away from it, and most of them did — the ship settled tail-first and burned upward, and people jumped from windows a few metres above the ground.
The second is that the fire was investigated twice, at the same time, by two governments with opposed interests, and they reached the same conclusion.
What the inquiries found
The United States Department of Commerce convened a board of inquiry; Germany convened its own commission, on which Hugo Eckener — the head of the Zeppelin company, and the most experienced airship man alive — served. The two worked in cooperation, and both took evidence about sabotage seriously enough to examine it.
The American report stated that the cause of the accident was the ignition of a mixture of free hydrogen and air, and that the theory of a brush discharge igniting that mixture appeared most probable. The German commission arrived at substantively the same place.
The picture is: the ship was carrying leaked hydrogen somewhere aft, the atmosphere was electrically charged after thunderstorms had already delayed the landing by hours, the mooring lines were dropped and wetted, and that earthed the airframe while the outer cover — a poorer conductor — remained at a different potential. A discharge across that difference is enough.
Eckener himself is the interesting witness here. His first public reaction was to suspect sabotage. He then examined the evidence and changed his mind, and he had every commercial and national reason not to, because an accidental ignition meant the design was at fault.
Eighty years of subsequent analysis has not overturned that finding.
The named suspect, and where he came from
The sabotage version has one persistent candidate: Erich Spehl, a rigger who died in the fire.
Spehl was not named in 1937. He was named in 1962, by A. A. Hoehling in Who Destroyed the Hindenburg?
The case Hoehling assembled is worth laying out, because it is a good example of a certain kind of argument. Spehl was a rigger, which gave him access to the area near Gas Cell 4 where the fire is thought to have begun — an area most of the crew could not reach. He was an amateur photographer. A dry-cell battery of the sort used for a camera flash was reportedly found in the wreckage. His girlfriend was said to have anti-Nazi and communist associations. And there were reports of a later Gestapo interest in him.
Hoehling was candid that this was circumstantial, and it is: every element establishes access or association rather than an act. Michael Mooney's The Hindenburg in 1972 named Spehl again with a different motive attached — a revulsion at the technological age rather than politics — which tells you something about how firmly the motive was established.
Subsequent examination has generally found the evidence against Spehl weak. He is a plausible person who was in a plausible place and who cannot answer.
The lawsuit
There is a coda to the Spehl theory that is genuinely strange and rarely mentioned.
Mooney's book became a Universal film in 1975, and Hoehling sued the studio, arguing that his work had been copied. The case reached the United States Court of Appeals for the Second Circuit, which ruled against him in 1980.
The reasoning is the point. The court held that copyright does not protect historical facts or interpretations, that these belong to the public domain, and that allowing a historian to own a theory would obstruct the writing of history, since each generation must be free to draw on the insights of the past.
So the man who invented the case against Erich Spehl went to court arguing it was his, and lost on the ground that a historical theory, once published as history, cannot be owned by the person who made it up. The theory had become a fact about the world in exactly the way its author needed it not to be.
The helium argument
The other durable version concerns not a bomb but a policy.
Helium is non-flammable and the United States controlled effectively the entire world supply, from natural gas fields in Texas, and restricted its export by statute. The Hindenburg was designed so it could use helium, and flew with hydrogen because it could not get any.
That much is accurate and is not disputed. The conspiracy version extends it: that the embargo was maintained in the knowledge that it left German airships flying on a flammable gas, and that Washington was content to see the programme fail.
The weaker part of this is the inference about intent. The export restriction long predated the Hindenburg and was framed as protection of a strategic material with obvious military value, in a decade when Germany was rearming openly. Declining to sell a strategic gas to a hostile rearming power is not a subtle policy that requires a hidden motive.
It is also worth noting what it would have meant if Germany had got helium. Helium gives roughly ninety per cent of hydrogen's lift and is expensive, so the ship would have carried fewer passengers at higher cost. The embargo shaped the disaster by determining what was in the gas cells. It did not require anyone to want the ship destroyed.
The paint theory
A third explanation deserves mention because it came from a credentialled source and has been tested more rigorously than either of the above.
In 1996 Addison Bain, a retired NASA hydrogen specialist, proposed that the hydrogen was largely incidental and that the real fuel was the outer cover — cellulose nitrate doped with reflective compounds including iron oxide and aluminium, a combination with a superficial resemblance to solid rocket propellant.
It is a genuinely interesting idea and it was checked properly, which is the useful part. Samples of the actual painted fabric were burned and compared against deliberately propellant-like formulations. The fabric burns, but slowly — orders of magnitude too slowly to propagate a fire across a two-hundred-and-forty-metre hull in the roughly thirty seconds the film records. Analyses of the energy available at the proposed ignition point found it insufficient as well.
The cover certainly burned. It was not what made the fire fast. Only the hydrogen accounts for the speed.
Why sabotage keeps its appeal
Partly because the disaster was so visible. It happened in front of a press pack, was filmed from several angles, and produced a radio recording so distressing it is still quoted. An event that public seems to demand a proportionate cause, and a static spark is not proportionate to anything.
Partly because of what the ship was. A swastika-marked flagship of Nazi Germany destroyed in front of American cameras invites a political reading almost automatically, and 1937 was a year when political readings were cheap.
And partly because the technical account is genuinely unsatisfying to hear. It requires accepting that a leak nobody located, meeting a charge nobody measured, ended the airship era in half a minute — and that the two governments least inclined to agree about anything examined it and agreed.