Jack interviews attorney and historian Catherine Grace Katz about her new book, Shadow Before the Flame: The Hindenburg Disaster and the Prelude to War. They discuss how a 1925 U.S. ban on helium exports required German airships to fly on flammable hydrogen, leading to the famous 1937 explosion over New Jersey. They also cover the Nazi takeover of the struggling Zeppelin company and the subsequent use of its airships as propaganda tools, and the later controversy surrounding whether to sell helium to Germany even after Congress relaxed the export ban. Katz closes by noting parallels to AI and other dual-use technologies, the necessity of balancing civilian risk against potential benefits, and the hubris that often accompanies large-scale innovation.
Mentioned:
Catherine Grace Katz, Shadow Before the Flame: The Hindenburg Disaster and the Prelude to War (Viking, September 2026)
Catherine Grace Katz, The Daughters of Yalta: The Churchills, Roosevelts, and Harrimans: A Story of Love and War (Houghton Mifflin Harcourt, 2020)
Emily Velasco, “History’s Mysteries: Caltech Professor Helps Solve Hindenburg Disaster” (Caltech, May 17, 2021)
“Hindenburg: The New Evidence,” NOVA (PBS, May 19, 2021)
Franklin D. Roosevelt, “Recommendation on a Policy for Helium Export,” letter to Rep. Lister Hill (May 25, 1937)
Franklin D. Roosevelt, “Statement on the Export of Helium” (May 11, 1938)
This is an edited transcript of an episode of “Executive Functions Chat.” You can listen to the full conversation by following or subscribing to the show on Substack, Apple, Spotify, or wherever you get your podcasts.
Jack Goldsmith: I’m Jack Goldsmith, and our topic today is a revolutionary technology with the potential to transform civilian life and military power, and the international scramble to regulate it. I’m not talking about artificial intelligence. I’m talking about Zeppelins.
And my guest today is Catherine Grace Katz, an attorney and historian who’s got a new book called Shadow Before the Flame: The Hindenburg Disaster and the Prelude to War. Catherine, thanks for talking with me.
Catherine Grace Katz: Thank you so much for having me on the show. It’s great to chat with you.
So the Hindenburg is a story that lots of people have heard of. Why write a new book about the Hindenburg story?
This is a story that kind of caught my eye somewhat accidentally, and it has its origins in watching a Christmas movie with my family a couple years ago. We were watching the movie A Christmas Story. You remember Ralphie, who wants his Red Ryder BB gun, while his little brother Randy receives a Zeppelin toy for Christmas and is thrilled.
And after watching the movie, my own younger brother Oliver, who loves aviation, just started talking about how incredible it was that people used to fly on these. And can you imagine what it would be like to look up and see one? And a beat later, he says, Catherine, you should write a book about the Hindenburg disaster.
And so that’s how the story first came to mind for me. But it’s kind of squarely in the area that I’ve always studied as a student, and then as a historian writing The Daughters of Yalta, about 1945.
That was your last book.
Yes. But the story just had so much relevance to me for the time that we are living in today: kind of the geopolitical moment, the technology moment, the media moment. All these different things seem to funnel through the story of the Hindenburg disaster, which I don’t think people realize, because it’s this event that sort of hangs in our consciousness, sort of like the Titanic of the skies. And yet when pressed, people barely know anything about it.
Right. And that would be true of me before I read this book. So talk about what is this technology, and tell us about the history of it, and tell us where it was basically by 1937.
When we think of the Zeppelins, we kind of think of airships as this sort of odd blip in the history of aviation. But actually, they’ve been around since the turn of the century. Count Ferdinand von Zeppelin invents them in southwestern Germany.
It’s the first rigid airship: unlike a blimp, where the shape is held by the pressure of gas inside of an envelope, this is a rigid frame with gas cells inside, covered in a canvas cover, held taut by the silver-like glue-ish paint. So that’s why it has this very silvery hue. People initially made fun of him, called him the crazy count, ridiculed his early Zeppelins as flying white sausages because they looked like Bavarian wurst.
But quickly, the technology really took off, pun intended, and they were used as weapons during World War I to bomb cities like London and Paris and Antwerp as the first instruments of aerial bombardment. This lasted until about 1917, when airplanes caught up in their range, their ability to fly faster, higher than Zeppelins and shoot them down. But after World War I, they really became a very popular civilian technology for long-distance travel, which was something that airplanes could not compete with at the time.
The first transatlantic flight between Europe and the United States occurs in 1919 with an airship actually made by the British. That same type of nonstop transatlantic flight for passengers was not possible until the jet age in 1959 by airplane. They are so popular that the Germans are building them, the Brits, the French, the Italians, and the Americans.
Lighter-than-air aviation is a huge part of the U.S. Navy at the time, and they actually have flying aircraft carriers, if you can imagine that, where airplanes fly up, hook on, and get winched up inside. But the Germans are just, you know, head and shoulders above everyone else in their engineering. The other countries have disasters with their airships, but the Germans—no one’s suffered so much as a scratch on board since the end of World War I.
And they’re conducting these amazing flights with the Graf Zeppelin in 1929. They do around-the-world flight. They start doing scientific expeditions to the Arctic in the early 1930s, regular passenger service to both North and South America.
And so by the time the Hindenburg, the Graf Zeppelin’s sister ship, is built in the mid-1930s, this is incredibly popular, but also somewhat commonplace mode of transportation for people who can afford it.
So let me ask you: you said that the U.S. Navy was still using these, but you said that they had basically lost their military significance with the rise of piloted heavy aircraft. Did they still, in the mid-’30s—I mean, were they still thought of as having military strategic or tactical significance?
To some degree, yes. So not for actually bombing cities. So kind of in that capacity, it lost its military significance, but they were used for scouting and reconnaissance and also for extending the range of airplanes.
So if you’ve watched the movie Indiana Jones and the Last Crusade, and you may remember Indy and his dad flying in a Zeppelin, they’re pursued by the Nazis. They jump into an airplane that’s hanging below the airship, cut the connection, and fly away. That was a real capability that the U.S. Navy had. So while airplanes couldn’t fly that far at the time, based on what kind of fuel they could carry, how fast they could go, kind of being transported by an airship by the U.S. Navy could extend the range of airplanes. And so it was not a super useful technology because they only had a few of these with a few planes that could be inside, but it was a natural capability, and also for, like, overflight protection of ships.
(5:15) Okay. So talk about the U.S. role in this. The disaster happens in 1937, but even before that, the United States played a critical role in controlling this technology, which I think is a big theme in your book. Can you talk about that?
Absolutely. So there are only two gases that are capable of lifting something as large as a Zeppelin. The one choice is hydrogen, which has the greatest lift capacity. It’s the lightest gas. It’s very cheap, widely available, but crucially, it’s extremely flammable. On the other hand, you have helium, which is a little bit heavier, much, much more expensive, but an inert gas, so it’s not flammable. But the problem is that it’s only been discovered in the United States in the Southwest as a byproduct of natural gas extraction and, at the time, nowhere else in the world.
Since then, it’s been discovered in other places like Russia and Qatar, places that have very unstable supply chains leading to continued issues with helium availability. But in the 1920s, Congress passes the 1925 Helium Control Act, which bans any export of helium, declaring it a strategic national natural resource. And so you see this very early case of export control laws involving helium.
The Germans then lobby to find some sort of exception to the law that Congress has passed. They actually find a lot of sympathy publicly for getting helium to make flying on a Zeppelin even safer, including from the White House. But this is a law that Congress has passed. So Germany is left with no choice but to either scrap the program entirely or to engineer around the danger of using hydrogen.
And why did the 1925 Act ban the export? Were they worried about this particular issue?
Well, it was a very scarce natural resource. You need a ton of helium to be able to fill even just the handful of airships that the United States Navy has—the USS Akron, the USS Macon, the USS Los Angeles—and a few other smaller lighter-than-air crafts. There’s also a domestic program with Goodyear based in Akron, which is building a lot of these for the United States Navy.
And so given the scarcity of the resource and how expensive it is to extract and export, the Congress decides that this is too valuable to allow any portion of it to go abroad.
Okay. So it’s the middle 1930s, and FDR, Franklin Roosevelt, is president. Talk about his role in this. He plays an interesting role throughout the book.
Little-known fact about FDR: he was actually a huge lighter-than-air aviation enthusiast. He had first taken a ride on an airship at the end of World War I when he was Assistant Secretary of the Navy, and he goes over to France and has a chance to fly in an airship that the French had built for scouting purposes during World War I. He takes a ride.
It goes about 1,000 feet, takes some time at the controls, and really enjoys it. After the war, he decides that he and some friends are going to start an airship company in the U.S. for domestic, kind of civilian travel. He thinks it’s the next great thing in engineering compared to airplanes, which are seen as very dangerous at the time.
And at one point, he learns that his mother has taken a plane while traveling in Europe, and he chides her, you know, why did you do that? They’re very dangerous. Just wait a few years, and you can travel in comfort and safety in one of my airships.
The company is ultimately not viable economically, so it folds, but he doesn’t lose his enthusiasm for it, and he actually has a really great relationship with the head of the Zeppelin company, named Hugo Eckener, who visits him at the White House on several occasions, including on the first flight of the Hindenburg in 1936, which is not Eckener’s first visit to the White House, nor the first time he’s met an American president. He’s actually visited the White House as early as in the mid-1920s, when he delivers the USS Los Angeles, which was originally a reparations payment that Germany built a Zeppelin for the U.S. Navy as part of the reparations payments. So he’s a very popular fixture in Washington, and he and Roosevelt have a very good relationship, and Roosevelt personally supports these airships and ultimately wishes that he could do something to change the law, but ultimately cannot.
So this person tries to get Roosevelt to change the law so that the Germans can get access to them. And he was sympathetic, as you just said, but decided basically for political reasons that he wasn’t going to stick his neck out and try to get Congress to change the law.
Exactly. I mean, there were just too many other things that he felt were political imperatives where he wanted to put the chips on the table. This was ultimately not one of them. He respects the separation of powers in this regard, and just thinking about kind of a number of other things that were much more pressing for him to pass that were controversial during the New Deal administration. This is kind of a nice-to-have, but not the top of his list.
(9:41) And just scope out a little bit and tell us what’s going on in the world. This is the middle of 1937. Hitler is in power, and how is Roosevelt thinking about that? How was Congress thinking about that? And how did the discussion about whether to give the Germans—for the Hindenburg, I guess, or maybe for all of the Zeppelins—helium instead of hydrogen, which as you say was more dangerous—how did the world political situation inform here?
It definitely impacts it. You know, thinking about kind of where Roosevelt wants to, you know, really put his chips down, looking at kind of the rising concern from Germany, it’s not a politically expedient or kind of strategically smart thing to do necessarily, because of alarming things that have been happening in Germany over the last couple of years. The Zeppelins had predated the Nazis significantly.
They were really the first thing that was popular internationally that was German after World War I, during the Weimar era. But the problem is they’re incredibly expensive to build, and the Zeppelin company’s out of money. To be able to carry more passengers, the Zeppelins have to become exponentially bigger to offset the additional weight and increase the amount of gas that they are using.
And so they are desperately in need of a cash infusion from the German state. Germany, through the Ministry of Aviation and the state airline, Deutsche Lufthansa, take a majority stake in the Zeppelin company, rebranded Deutsche Zeppelin-Reederei, repaint the fleet with the new standard of Germany, which of course is the swastika flag at the time.
Interestingly, Hitler is not a huge fan of the Zeppelins. He can’t get past the fact that they’re filled with hydrogen. He’s a big fan of flying in airplanes, but he never sets foot on a Zeppelin. Hermann Goering, even though he’s financed this, kind of sees it as a somewhat outdated technology already, you know, says, I can build 10,000 airplanes for the cost and time it takes to build one Zeppelin. Why would I do this?
But it truly is a propaganda tool that is embraced by Joseph Goebbels, who wants to piggyback off on the soft power projections that the Zeppelins offered Germany to burnish their reputation as a leader in engineering, transportation, technology, as this thing that is so popular internationally about Germany, where Germany’s suffering from reputational issues anyway.
But 1937 is this odd moment where there is a lull in fear about Hitler, because he’s kind of gone quiet. And it seems almost as if he’s achieved the things that he says that he set out to achieve in restoring German national pride and rearmament.
1933, he becomes chancellor. 1934, he consolidates power at the Night of the Long Knives. 1935, passes the Nuremberg race laws. 1936, he remilitarizes the Rhineland and tears up the Treaty of Versailles. But 1937, things are kind of quiet. So it’s at this odd time where people are thinking that maybe Hitler’s just going to be a normal world leader after all, after all of the alarming things that have been happening in Germany the last few years. By comparison, even though there are crackdowns on civil liberties, the press, a huge anti-Semitism towards Jews, internationally, it seems like maybe Hitler’s settling down.
But it would have been controversial for Roosevelt to go to Congress to try to get an exemption or a new law in 1937 to give the Germans access to helium, even for the supposedly benign transportation purposes that the dirigibles were serving then. Is that right?
I think it depends on who you ask. I think there was a real split of people who were very clear-eyed about the threat of Germany, whether that was Ambassador Dodd, who was on the ground in Berlin, whether it was the Secretary of the Interior, Harold Ickes, who was very skeptical of Hitler and very much attuned to his broader machinations early on, whereas other members of the government maybe not quite so heightened in their concerns about Hitler.
I think that it maybe would have been more of a concern, you know, why are we spending all this time and attention on something abroad when we have so many issues internally that we need to deal with? But I think that you have a real split reality of people at the time who kind of take and understand the menace of Hitler for what it is compared to those who are kind of saying, well, this isn’t as bad as it’s been the last few years. And there’s just so much sentiment that’s, you know, against any kind of global conflict that, you know, the spirit for kind of, you know, simmering down of anything inflammatory is very much in favor.
So, you know, this could have been something where there could have been collaboration between Germany and the United States that actually may not have been so controversial because people didn’t see the Zeppelins really as Nazi instruments, and they really saw them as this kind of dream machine of the Weimar Republic era.
And yet Roosevelt wouldn’t stick his neck out on this.
No, he would not.
(14:05) Okay, so tell us about the fire and the explosion. What role did hydrogen play in the explosion?
The hydrogen is the whole story here. If it had been filled with helium, nothing would have caught fire in that way. I mean, there could have been other structural issues that other countries had. The United States had its own hydrogen-filled airships that did suffer some structural malfunctions and disasters. But for the case of the Hindenburg, it was actually a mystery for quite a long time why the fire had occurred. You know, of course, as soon as some hydrogen catches fire, all of it’s catching fire, and this thing is filled with millions of cubic feet of hydrogen.
So in the initial aftermath of the disaster, there was immediately an investigation where the United States and German experts convened, including people who had been the key engineers building the airships. The NYPD bomb squad is called in to go through the wreckage to see if there was an incendiary device, to see if it was sabotaged. But at the end of the day, they concluded it was almost certainly not sabotaged, and it was almost certainly because of kind of structural and engineering issues.
And they didn’t have a way to test it at the time, but the leading theory by the people who knew the most about this technology was that there was some charge differential, and a static discharge had somehow ignited hydrogen that had gone free from one of the gas cells. Not until 2021 that a professor at Caltech, in cooperation with the show NOVA, actually tried to run some experiments that were not possible at the time to recreate the conditions of the Zeppelin and the atmospherics at the time. They were landing in the middle of a storm.
What probably happened is the gas escaped because a shear wire probably broke on what was likely a too-tight turn going into the landing. Having some gas come out is not necessarily cause for alarm. In flight, they could actually patch it. But as long as there’s a current of air sweeping the hydrogen away, it’s not catastrophic. But as it comes to a standstill, this leaking hydrogen starts to build up. And as one of the safety precautions, the engineers had actually designed the Hindenburg so that the cover and the frame didn’t touch anywhere.
They were held apart by non-conductive twine and wooden dowels. So what ended up happening is that in many, many places on the airship, the professor discovered that the Hindenburg became a gigantic capacitor, like on a switchboard in many parts, where you have a huge charge differential as energy builds up across this differential as the skin and the frame take on more and more positive versus more and more negative charge. And as soon as there’s a conductive bridge formed between them, not necessarily with a physical object, but something like gas that is conductive, then you have that equalization of charges, which releases energy, which causes a spark, which as soon as some of the hydrogen catches fire, all of it’s going to go up in flames.
(16:45) So this crash basically ended the industry. There was a discussion in the United States in 1937 and a new law, which I want you to tell us about, that made it theoretically possible to give helium to the Germans. Talk about the ‘37 law, the decisions made inside the Roosevelt administration, and then the impact on the industry.
So it’s kind of surprising that the Hindenburg disaster didn’t actually immediately kill the airship and Zeppelin industry. There was a lot of goodwill and outpouring of sympathy for Germany at the time. You’ve got FDR, the King, the Pope sending condolence letters to Hitler. It’s been an international tragedy. It’s not just Germans who were killed. It’s also Americans, other Europeans.
Surprisingly, two-thirds of the nearly 100 people on board do actually survive, which is astounding to think about when you see the conflagration and how quickly, just in 34 seconds, something as big as the Capitol building is just incinerated. But there’s a huge groundswell of support from the American people, really voiced by Eleanor Roosevelt, actually, who learns of the tragedy as she’s flying from the West Coast back home. She’s changing planes in Chicago and hears about this disaster and says, this is such a tragedy, this is a terrible setback, but this is part of being part of humanity, where there will be setbacks, there will be tragedies, but we learn from them and we move forward and we don’t let this stop us from pressing forward with new innovations that have the potential to change the world for the better.
This is very much the attitude of the American public, so there’s a lot of sympathy to change the law. Congress does actually—
Just to be clear, to change the law to give helium—
To allow for the export of helium.
Was it decided basically that hydrogen—that this industry could not work relying on hydrogen and had to have helium? Is that fair?
Exactly. Yes. No one would want to fly on a Zeppelin again. It wouldn’t be responsible to fly on one that was filled with hydrogen.
Congress does, in the middle of 1937, pass an amended law that does allow for the export of helium, notably for countries for whom helium will not hold military importance. It’s a very important phrasing where it’s not necessarily that helium will play a military purpose, but that it could have the potential for military importance. Ultimately, Congress changes the law. FDR is happy about this. He supports the export of helium.
The law is structured so that final approval has to come from the National Munitions Control Board. They vote unanimously to allow Germany to purchase helium. They say it fits with the wording of the statute. But at the end of the day, one person has the final say, and that’s the Secretary of the Interior, Harold Ickes. He’s the one responsible for the national stockpile of helium, and he says, I’m looking at this law. It’s not possible that this could not have military importance for Germany.
Yes, Zeppelins and airships are obsolete in the original use for military purposes of dropping bombs, but we’ve just budgeted, in the national defense budget, a new airship for the Navy. We use them for scouting, for overflight protection. If Hitler is over there assuring me that they’re not going to use it for military purposes, that inherently has to mean that helium still has military importance to Germany.
Harold Ickes, in a strict statutory reading, vetoes the export. Germany is not allowed to purchase helium, which is actually sitting in containers ready for them to take away. He says no. Despite additional lobbying, he does not change his mind.
Germany then is forced to decide whether they’re going to continue to build the new Zeppelin that was already underway at the time of the Hindenburg and use hydrogen. They actually go ahead. It begins to fly in 1938, and they do use it for military purposes. They use it to scout out military installations and British radar installations around the British coast. Some of the crew originally on the Hindenburg is on this flight. They don’t know exactly that’s what they’re doing. There are other actors from the German government on board assessing this, but that is ultimately the last purpose of the Zeppelins in Germany before the program is dismantled and the Zeppelins are blown up on the third anniversary of the Hindenburg disaster and used for scrap.
(20:50) Catherine, what’s your main takeaway about this episode for modern times?
I think as we assess whether it’s export control, think about these dual-use technologies and technologies like AI that have incredible uses to benefit mankind, while also balancing against the enormous risks that they offer, especially if it falls into the hands of adversaries with bad intentions. Balancing also the hubris of invention and people’s inability to really assess downside risk when they’re advocating for a technology that they’ve staked their career and their reputation on. I think we have to remember that at the end of the day, whether these decisions are made on an international geopolitical level, national regulatory level, ultimately the effects of those decisions are felt by regular people like you and me.
We are able to reap the benefits, but also sometimes suffer the consequences of those decisions. It’s been a privilege for me to be able to put the story of the humanity of the individuals impacted by these decisions and the Hindenburg disaster back in full focus. That’s my purpose in telling the story. I really hope that that story of humanity set against the backdrop that should resonate with people today very much comes through front and center.
It does. Thanks very much, Catherine.
Thank you so much for having me on the show.
