The Hindenburg burned at Lakehurst on 6 May 1937, and two governments investigated it separately. This film is about what they did, and about the fact that they reached the same sentence.
You have seen this. Almost everybody has. It is one of the small number of pieces of film that a person can be said to have seen without ever having chosen to watch it. An airship is coming down towards a mast on a wet field in New Jersey.
It is evening. There has been a thunderstorm and the storm has passed. Ropes drop from the bow. And then, on the top of the ship, a little forward of the tail fin, there is a light, and in fifteen seconds the fire has run thirty metres forward along the hull, and about half a minute after that first light the ship is on the ground.
Ninety-seven people were on board. Sixty-two of them walked, crawled or were carried out of it. That is the part you have seen, and this film is not going to spend thirty minutes on it, because there is nothing left to find in thirty-four seconds of film that has been looked at for eighty-nine years. What happened next is the part almost nobody has seen.
Four days after the fire, in the main hangar on that same field, the United States Department of Commerce opened public hearings, and they ran for nineteen days. A German commission came and sat in the same room, and from the fourth day its members gave evidence as witnesses. Two governments, working from the same wreck and the same witnesses, wrote two separate reports. They had, between them, every reason to disagree.
And they did not. They put the start of the fire in the same place, over the same two gas cells, and they named the same mechanism — a mechanism that leaves no residue, no fragment, no scorch mark, and no witness who can say they saw it. This is what they did in those nineteen days, and what it means that this is the answer they arrived at.
EIGHT HUNDRED AND THREE FEET THE SHIP, BEFORE Start with the machine, because the machine is the reason the fire mattered. The airship was placed in service early in 1936. It carried the builder's number LZ 129 and it was built by the Luft Schiffbau Zeppelin at Friedrichshafen, an organisation which by then had previously built one hundred and eighteen airships. It was eight hundred and three feet long.
It was one hundred and thirty-five feet across at its widest point. It held just over seven million cubic feet of gas. The passenger accommodation was not slung underneath — it was inside the hull. Those are the numbers people remember.
Here is the number that matters more, and it comes from the American report's own section on the ship's record. In its nine months of operation in 1936, this airship made more than fifty-five flights. It flew two thousand seven hundred and sixty-four hours. It cruised one hundred and ninety-one thousand, five hundred and eighty-three miles.
It crossed the ocean thirty-four times. It carried two thousand seven hundred and ninety-eight passengers and more than three hundred and seventy-seven thousand pounds of mail and freight. All without mishap. That is the report's phrase.
In March 1937 the German government renewed the airworthiness certificate, reporting that all of the safety devices had been inspected and found satisfactory. Six weeks later the ship left Frankfurt on the first scheduled crossing of the 1937 season, and it was due at Lakehurst on the morning of Thursday the sixth of May. It was late. Headwinds over the Atlantic put it behind, and its arrival slipped to the evening.
SEVEN MILLION CUBIC FEET OF HYDROGEN SIXTEEN CELLS To understand what both commissions concluded, you have to know how the ship held its gas, because their conclusion is a statement about a specific part of it. The hull was a framework of duralumin girders, braced with wire. That framework was divided by wiring into sixteen compartments, and into each compartment went a gas cell — a bag, made of a film laid between two layers of fabric, with netting around it so that no sharp edge of the structure could reach the bag. The cells were numbered from the stern forward: one at the tail, sixteen at the nose.
They were not sealed things. Fabric leaks, and the report says how much: about one litre per square metre per twenty-four hours. That is a rate the investigators would later look at and dismiss, and we will come back to why. Between every two cells there was a shaft.
The shafts ran vertically, from the walkway at the bottom of the ship, up through the axial corridor in the middle, to the top of the hull, where they opened under hoods into the outside air. If gas was released from a cell — deliberately, through a valve — it went up a shaft and out of the top of the ship. There were fourteen automatic valves and fourteen hand-operated ones, and the hand-operated ones for eleven of the cells were wired to a single master wheel in the control car, so that the officer of the watch could vent them all together. And the gas itself.
Hydrogen is colourless. It is odourless — the report notes that the only way you could smell it at all would be through impurities left by the process that made it. It diffuses in every direction. And a mixture of hydrogen and air will burn across an enormous range: the report gives the flammable limits as probably between four and a half per cent and sixty-two per cent hydrogen.
Four and a half per cent. That is the number to hold on to.
TWO TO THREE HUNDRED CUBIC METRES WHAT THE INDICATOR COULD NOT SEE In the control car there were meters. They were fed by electrically actuated units in the axial corridor and they showed the pressure, and therefore the relative fullness, of each of the sixteen cells. If a cell was losing gas, that is where you would find out. Here is the American report on those meters, in its own words: "The accuracy or sensitivity of this system was not definitely established." And then, immediately after: "An appreciable amount of gas might have been able to escape before such escape would show on the visual indicator unless that indicator was kept under close observation." And then the report calls a witness, and the witness is Hugo Eckener — the man who had run the Zeppelin company, who had commanded the Graf Zeppelin around the world, and who was, by a distance, the most authoritative airship man alive.
According to Eckener, a cell could lose at least two hundred to three hundred cubic metres of gas before the indicator would show the loss. The report adds a sentence to put that in proportion, and the sentence is careful: such an amount is only a very small proportion of a cell's content. Both things are true at once, and both matter. Three hundred cubic metres is a trivial fraction of a cell that holds hundreds of thousands.
And three hundred cubic metres of hydrogen loose inside the top of a ship is a great deal of hydrogen. That is the whole of what the investigators had, on the question of whether the ship was leaking: an instrument that they could not certify, and the most experienced man in the field saying it would not have told you.
THE THUNDERSTORM ENDED AT 4.45 THE AFTERNOON OF THE SIXTH The weather is in the record in unusual detail, because the United States Weather Bureau was part of the investigation and brought its maps. At half past seven that morning there was a disturbance over central New York and north-eastern Pennsylvania, with a cold front running south-west from it into West Virginia. Through the day that front moved east across Pennsylvania at twelve to fifteen miles an hour. It passed Lakehurst shortly after half past three in the afternoon.
The station's own records show a thunderstorm beginning at 3.43 and ending at 4.45. The report is careful not to make the weather into more than it was. Telegraphic reports, it says, indicate the thunderstorms in and to the west of New Jersey were not severe, nor were they of a well defined squall character. And it summarises: the thunderstorms in eastern New Jersey were of a local character and not severe.
So this was not a storm anyone would refuse to fly in. It was a wet, unsettled, ordinary spring evening on the New Jersey coast, with a front that had just gone through and the air behind it still deciding what to do. The ship, meanwhile, had already been over the field once. It passed Lakehurst, went off to cruise along the coast for a few hours, and then came back — retracing its course from Tuckerton to the naval air station.
It was waiting for the weather.
FOUR MESSAGES, ON THE CLOCK FOUR MESSAGES What passed between the ship and the ground while it waited is in the report, quoted, with times. Here it is, in order. At 4.42 in the afternoon, the commander of the station radioed the ship: "Conditions still unsettled recommend delay landing until further word from station advise your decision." At 4.52, the commander of the ship replied: "We will wait till you report that landing conditions are better." At 5.12 the station sent a full weather observation — the thunderstorm over the station, ceiling two thousand feet, visibility five miles to the westward, surface wind west-south-west eight knots gusting to twenty. At 5.22, the station commander radioed: "Recommend landing now." And at 6.08, the last message the station sent: "Conditions definitely improved recommend earliest possible landing." The ship acknowledged it.
Seventeen minutes later the ship was on fire. Now — and this matters, and the film is going to be explicit about it, because the sequence you have just heard is the easiest thing in this entire record to misuse. Neither commission found fault with that exchange. Neither found fault with the landing.
The German report says the landing was executed in a completely normal manner in the opinion of all experts, that the behaviour of the whole crew before and during the catastrophe was exemplary, and that there is no indication the ship had been in anything other than faultless technical condition when it began its approach. The messages are in this film because they are in the record and because they tell you what the evening was actually like: a station commander watching a front clear, and a ship's commander waiting to be told it was safe. Both of them made the judgement anyone would have made. That is the point of including them, and it is the whole point.
RELATIVE HUMIDITY 98 NINETY METRES The approach is documented from both sides, and between them the two reports give you the manoeuvre almost minute by minute. The ship came in, found the wind had gone round to the south-east, turned away to port to come back into it, and made its second turn to approach the mast from the north. During the large turn, about ten minutes before the ropes went down, gas was valved from the five forward cells — twice for fifteen seconds, once for five. That is a deliberate release, and it is routine: you valve gas forward to bring the nose down.
The ship was still tail-heavy. So six men were sent forward from the midsection to the bow, to weigh the nose down with themselves. Water ballast went over the side three times from frame seventy-seven — three hundred kilograms, three hundred again, then five hundred. Eleven hundred kilograms, about two and a half thousand pounds of water, inside two to three minutes.
About two minutes before the bow ropes were dropped, all four engines went full astern for roughly a minute to stop the ship. And then the ropes went down. The control car was at ninety metres — a little under three hundred feet. Two things about that moment are worth holding.
The first: everything in the paragraph you have just heard is normal. It is what landing an airship looks like. The second: it had been raining. The ropes were manila, and they were wet, and they were now lying on wet ground with a metal ship attached to the other end of them.
6.25 P.M., EASTERN STANDARD TIME HALF A MINUTE The German commission established the sequence of the fire from the testimony of witnesses, and it was honest about how hard that was. The testimony about where the fire started, it says, is to a great extent widely divergent — because the fire spread so fast, because the witnesses were standing in different places, and because the ship was so large that no one person could see all of it. Weighing all of that, the commission reached this: The first fire started on the topside of the ship, in front of the leading edge of the vertical stabiliser, over gas cells four and five. From there it spread forward about twenty to thirty metres in the course of some fifteen seconds, until the first explosion took place.
And between the first appearance of the fire and the contact of the main body of the ship with the ground, there elapsed about one half minute. Thirty seconds. Of the ninety-seven people on board, thirty-five died. Twenty-two of the sixty-one crew, and thirteen of the thirty-six passengers.
One man on the ground crew died of his burns. Sixty-two people got out of a burning hydrogen airship in half a minute, which is the fact from that evening that almost never gets said out loud. The film is not going to linger here. There is nothing to learn from lingering, and what happened to those thirty-six people is not an argument.
NINETEEN DAYS OF HEARINGS THE HANGAR On the seventh of May — the next day — the Secretary of Commerce issued an order under the Air Commerce Act of 1926, and designated three men to investigate. South Trimble junior, the department's Solicitor. Major R. W.
Schroeder, Assistant Director of the Bureau of Air Commerce. Denis Mulligan, chief of its Regulation and Enforcement Division. Around them they put technical advisers, and the list is worth hearing because of what it tells you about how seriously this was taken. Commander Rosendahl of the United States Navy, who commanded the station and who had watched the ship burn.
Colonel Chandler and Colonel Lincoln of the Army. Colonel Hartney, technical adviser to the Senate Committee on Commerce. Gill Robb Wilson, director of aeronautics for the state of New Jersey. Grover Loening, aeronautical adviser to the United States Maritime Commission.
The German ambassador was invited to send an observer and sent the military attaché. Public hearings opened on the tenth of May in the main hangar at the naval air station — the enormous shed the airships were kept in, a few hundred yards from a wreck that was still there — and ran until the twenty-eighth. They moved to Asbury Park, and then to New York. On the fourth day the German commission arrived.
Eckener. Lieutenant Colonel Breithaupt. Professor Bock. Professor Dieckmann.
Doctor Dürr, the ship's designer. And from that day they sat as observers and gave evidence as witnesses. The United States Navy had its own board of inquiry running, and it kept an observer in the room throughout. Assistance came from the Navy Department, from the Bureau of Investigation at the Department of Justice, from the Weather Bureau, from the Bureau of Standards, from the New York City Police Department and from the Bureau of Explosives.
And — this is in the report — from newspapermen, newsreel representatives and photographers, many of whom had been eyewitnesses. The people who shot the film you have seen were also witnesses in the inquiry into what the film showed.
EVERYBODY WAS SAYING IT SABOTAGE The first thing they dealt with was the thing everyone was saying. It is worth being clear that the investigators did not wave this away. The report's own sentence is that the possibility that the cause is to be explained by premeditated or wilful act "has received active attention", and they broke it into two classes and went through both. External sabotage: an incendiary bullet fired at the ship.
A high-powered electric ray directed at it. An igniting composition dropped onto it from an aeroplane. Internal sabotage: the placing within the ship of a bomb or other infernal device. The finding is one sentence: "To date, there is no evidence to indicate that sabotage produced the grim result." That is where it sat in 1937, and it is worth saying that it is where it has largely sat since.
The theory has never entirely gone away and it has never acquired any evidence.
A MIXTURE, AND SOMETHING TO LIGHT IT TWO THINGS MUST BE PRESENT Having disposed of deliberate act, the board set out the frame it would use for everything else, and the frame is the best piece of thinking in the document. For an accidental cause, they wrote, two factors must be found together. There must be present a combustible mixture of hydrogen and the oxygen of the air. And there must be sufficient heat to ignite it.
And then: in the analysis of the evidence, the mixture and its ignition are treated separately. That is the whole method. Two questions, asked independently. How did free hydrogen get where air was — and what lit it.
They took the mixture first. Could it have accumulated by diffusion through the cell fabric? No. At about one litre per square metre per twenty-four hours, the board said, that characteristic of the cell walls would not account for a combustible accumulation.
Could a valve have failed? Only one valve failure had ever occurred on the ship, when it was new, and it was an automatic pressure-relief valve which would not have been operating at the time. The board allowed that valves are mechanical devices and can fail, but no testimony showed it likely. Could it have been reduced ventilation — the ship slowed to a stop, its scavenging airflow gone, after that last valving six minutes before the fire?
Improbable, they said: the chimney effect of a six-knot wind at the ship's altitude in the final four minutes should have cleared practically all of it. Every mechanism they could name for getting hydrogen into the top of that ship, they knocked down. And yet their conclusion says a leak. Hold that.
ONE THEORY AT A TIME THE ELUSIVE SPARK Then the other half. What lit it. They began with the engines. Four Daimler-Benz diesels in cars slung outside the hull.
Could a spark, or a larger particle of carbon, thrown from an exhaust, have been carried into the ship? Much time was given to this at the outset of the investigation. It did not survive it. Friction.
If wires or structural members had come forcibly into contact — if something had broken — could the heat have made a spark hot enough? The report: "There is insufficient evidence to sustain a conclusion based upon this theory." Catalysis. There are metals which lower the ignition temperature of a hydrogen-air mixture. But, the report says, it does not appear that any such metal was in that part of the ship where the fire was first observed.
And finished duralumin — which the ship was made of — would not be expected to have material catalytic effect. Spontaneous combustion. "The evidence is inadequate to support this theory." Radio. Could energy have got into the structure from outside, through the stern cable?
Only if a powerful transmitter had been operating close by, and none was. Could the ship's own transmitters have set up a resonance inside it? Impossible — every transmitter on board had been switched off before the fire, the trailing antennas reeled in, the dynamotors shut down. The last message left the ship at ten past six, and it went out on the long wave.
And then the last one, and it is the one that shows you what kind of document this is. In the older type of gas cell fabric, which contained a rubberised element, you could make a static spark simply by tearing it. Did the Hindenburg's cells contain that material? The report says: as far as we could learn, they did not.
And then it adds the sentence that stands over the entire investigation: "Since virtually all of the cells were consumed by the fire, no test could be made of the cell fabric." That is what these men were working with. The fire had eaten its own evidence. Every question they asked about what was inside that ship had to be answered from testimony, from drawings, and from physics — because the object itself was a heap of wire on a wet field.
THE GRADIENT CROWDS AT THE FIN A WET ROPE AND A WET SKIN So what was left? The German commission went furthest here, and its argument is the most physical thing in either report. It is worth following slowly, because it is the answer. When an airship lands, it is hanging in the air with a charge on it — its own, and whatever the atmosphere has induced.
Then you drop ropes, and the ropes touch the ground, and the ship is earthed. The charge runs away down the rope, and the metal framework takes up the potential of the ground. Now think about the shape of that. The framework is at earth potential.
The air around it is not. The commission puts it like this: all the equipotential surfaces pass out over the upper edge of the grounded airship, and especially over the protruding parts of the stern — as for instance on the stabilising fins — an increased potential gradient results. The field crowds at the fin. It crowds at the fin because the fin sticks out.
And at Lakehurst that evening there probably existed, in the commission's words, strong electrical disturbances in the atmosphere. The wind had changed direction and temperature, which made a second thunderstorm probable. Under those conditions the gradient near the ground goes up. Then comes the part that makes it work.
The framework is metal and it earths in a fraction of a second. The outer cover is not metal. It is doped fabric, and it is a poor conductor, and its resistance is high. Treat the framework as a capacitor against the earth, connected through the landing rope, and the commission says its time constant runs anywhere from a thousandth of a second to many minutes depending on conditions.
Now put rain on it. A wet patch on the outer cover conducts reasonably well — and that patch is connected to the framework only through the resistance of the fabric underneath it. Its time constant, the commission says, amounts in value to seconds. Seconds.
So for a few seconds after the ropes go down, you have a ship whose metal frame is at ground potential and whose wet skin is not, with a fabric layer between them, in a field that is changing quickly, at a place where the geometry crowds the gradient — the fin. Between the wet spot, the framework and the earth, potential differences occur. And the commission's conclusion from that: Between ship and atmosphere, the occurrence of a brush discharge or St Elmo's fire could be well conceivable. And then this, which is why nobody saw it: "As a hydrogen-air mixture burns nearly without color, under the given circumstances the first ignition could have happened on the upper part of the vertical stabilizing fin and could have quickly spread to the leading edge of the fin on the ship's body." The flame was there before it was visible.
But the commission did not stop at the elegant part, and neither will this film. It wrote down the limit of its own argument in the next breath. The possibility of an ignition by St Elmo's fire cannot be set aside — "but it is premised on the presence of quite extraordinary gradients, unless assumptions are made which could hardly have been present in the case under question." That is a group of scientists saying: this is our answer, and here is what our answer requires, and we cannot show that it was there.
WRITTEN SEPARATELY THE SAME SENTENCE Two reports. Written separately, by two governments, in 1937, at a moment when one of them had every political reason to want the answer to be sabotage by its enemies and the other had every reason to be suspicious of a machine flying another country's flag over New Jersey. Here is the American conclusion, complete. "The cause of the accident was the ignition of a mixture of free hydrogen and air.
Based upon the evidence, a leak at or in the vicinity of cell 4 and 5 caused a combustible mixture of hydrogen and air to form in the upper stern part of the ship in considerable quantity; the first appearance of an open flame was on the top of the ship and a relatively short distance forward of the upper vertical fin. The theory that a brush discharge ignited such mixture appears most probable." Signed: South Trimble junior. R. W.
Schroeder. Denis Mulligan. And the German finding, on where the fire began: The first fire started on the topside of the ship and specifically in front of the leading edge of the vertical stabiliser over gas cells four and five. The same two cells.
The same fin. The same side of the ship. The same mechanism. Neither of them could prove the leak.
The Americans had just spent a chapter knocking down every route by which hydrogen could have got out, and then concluded that hydrogen had got out — because the fire told them so, and because a fire that starts on top of a hull and runs forward thirty metres in fifteen seconds is not starting in the open air. Neither of them could prove the spark. There was nothing to find. A brush discharge consumes nothing, leaves nothing, marks nothing, and in this case would have lit a flame you could not see.
What they had was a place, and a shape of an explanation, and the agreement of two sets of people who were not trying to agree. NOBODY WROTE THE WORD PROVED
It is worth being exact about what was and was not settled in the summer of 1937, because films about this have not always been. Sabotage: no evidence. That is a finding, and it has stood. The crew: no fault.
That is a finding too, from both commissions, and it has stood. The cause: a mixture of free hydrogen and air, ignited. That is the American board's flat statement, and everything downstream of it is hedged. A leak at or in the vicinity of cells four and five — "based upon the evidence", not observed.
A brush discharge — "appears most probable". On the German side, an ignition mechanism that "cannot be set aside" but which requires gradients the commission could not demonstrate were present. Nobody in 1937 wrote the word proved, and this film is not going to write it for them. The argument did not stop there, either.
From the 1990s onward there has been serious advocacy for a different account, in which the doped outer cover of the ship is itself the thing that burns, and the hydrogen only follows. That argument is not in these two reports, because it did not exist yet, and this film has been about these two reports. But a film that left you thinking the question closed in August 1937 would be lying to you by omission. What is remarkable about the 1937 investigations is not that they found the answer.
It is what they did with a case in which the evidence had burned. They stated the two things that had to be true. They went through every route to each of them, one at a time, and they wrote down which ones they had eliminated and on what grounds — including the ones they eliminated only weakly, and including the ones they could not test at all because there was nothing left to test. And then two of them, working separately, arrived at the same two gas cells and the same fin.
That is not proof. They said so. It is the closest thing to it that anyone was ever going to get from a machine that had turned itself and its own evidence into a heap of wire in thirty seconds, in front of more cameras than had ever been pointed at a disaster before, none of which showed the one thing that mattered — because the thing that mattered was invisible.
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