An M4, or four-rotor, Enigma machine, recovered from a bunker in Trondheim toward the end of World War II. It set a record for any Enigma machine at Sotheby's in December 2019.

What you see: A four-rotor (“M4”) Kriegsmarine Enigma cipher machine, in its original case. It sold at Sotheby’s New York in December 2019 for $800,000 against an estimate of $300,000 to $500,000, setting a new world auction record for an Enigma machine.

The expert: Cassandra Hatton, vice president and senior specialist for books and manuscripts at Sotheby’s.

Let’s start by explaining what an Enigma machine is. An Enigma machine is a machine used to encrypt messages. It doesn’t send messages. It simply encodes them so they can be sent in a secret manner. They were usually sent by Morse code. In order for encryption and decryption to function, you need two machines. The Enigma machine was not invented by the Nazis, but the Nazis chose to use it because it was the best model of encryption machine. Before the war, they were used in the commercial realm, to keep business secrets.

Were there different types or varieties of Enigma machine? When World War II broke out, the Nazis chose to adapt and use the three-rotor machine, also known as the E1. It was primarily used by the army. Three-rotors tend to be banged up. They were on the ground.

Were three-rotors the most common model of Enigma machine used during World War II? Those are the most common, which is not to say any are common. They’re the ones I see the most.

So, Enigma machines predate World War II and were used commercially. Were they available to the Allies? They were. My understanding is the Nazis had a contract with the companies that manufactured them. I don’t think the companies had a choice [to decline the German contract], but during the war they exclusively produced a more sophisticated machine than was previously available in the commercial realm. The Nazis swooped in when the machines were on the verge of having an extra layer of encryption invented, and bought it all out. If the Allies had a machine in their hands, they’d captured it.

The example that set the world auction record is a four-rotor Enigma machine. How is it different? The Nazis knew that the Allies were working to break the code, but they weren’t aware of the codebreakers at Bletchley Park. The commander of the German naval fleet, Karl Doenitz, was particularly concerned about it. He had a four-rotor Enigma machine developed in secret, to be used by the German navy. The body is slightly different. Both the three-rotor and the four-rotor are in an oak case, but the four-rotor has a handle on the side, so you can slide it into a slot on a U-boat so it doesn’t roll around. The majority of four-rotors were on U-boats, and the majority are trashed, rusted out, because of exposure to salt water and air. I’ve seen them completely rusted, with just the chassis surviving. To find a machine that’s complete and in fantastic condition is so rare, and to find one with a traceable provenance… it’s a unicorn. This is the unicorn of Enigma machines.

How did this four-rotor Enigma machine manage to survive in such good condition? The story is fantastic. We do know where the machine originated. It was in a bunker in Trondheim, Norway, in a major communications center. The crew had 15 of these machines.

Wow, 15? Was each four-rotor Enigma machine in that Trondheim bunker dedicated to a single U-boat, or could each machine only handle one message request at a time? A machine couldn’t handle more than one at a time.

How does the four-rotor Enigma machine work? When you open it up, you see that there are rotors inside–wheels. Each wheel has 26 positions. In the four-rotor, the wheels have letters, A to Z. Each wheel has to be set to a specific letter. Patched cables also have to be set in very specific ways at the front of the machine. For Machine A to encrypt the message, it has to be set up in a specific way. For Machine B to decrypt the message, the cables and the rotors must be set up in the same way. It takes 45 seconds to reset a machine, but during war, there’s no time for that. Each machine had a different setting, set up to speak to a specific machine.

But I don’t think this is the rarest form of Enigma machine. Didn’t they make a 10-rotor? That wasn’t used in wartime, really, and it’s not exactly a 10-rotor. There are double rotors, and I don’t completely understand how those machines function. I would compare a three-rotor to a Volvo. A 10-rotor is more of a Prius. I can change the oil in an old Volvo, but I can’t in a Prius.

How did this four-rotor Enigma machine leave the bunker? The bunker was sieged, taken by surprise. When a machine was captured, the first thing that the Nazis were supposed to do was destroy the machine–open it, smash the rotors, smash the keyboard, throw it in a lake. The most important thing to get rid of was the rotors. The secret of the rotors was not just in their secret positions. Each has internal wiring that’s different. If you can figure out the internal wiring, it all falls apart.

“It all falls apart,” meaning if you learn the way the rotors are wired, you can easily figure out whatever messages come over? Exactly. But if the rotors are destroyed, you can’t figure it out.

What happened to the other 14 machines in the Trondheim bunker? They did survive the war, but I think they were disposed of later. The fact that this machine’s rotors are in perfect condition shows they were taken by surprise. They were not able to destroy the machine. They [the people working in the bunker] were kept prisoner and forced to teach a Norwegian naval officer how to use the machine.

So this would have been after Vidkun Quisling was overthrown? Yes.

What happened to the four-rotor Engima machine after it left the bunker? After the war, Churchill ordered all types of Enigma machines destroyed. Most from the bunker were trashed. One member of the Norwegian naval forces took this one home and kept it. His son consigned it, and told me that kids in his village used rotor boxes to keep change in. This was something kept in his house, not hidden, just there. There was no sense they were not supposed to have it, or it was stolen.

Is that how most Enigma machines come down to us now? Someone kept it? It’s what I understand to be the case with every Enigma machine that comes to market. The majority were kept as souvenirs. Someone’s Swiss grandpa took one and kept it in the attic, or they’re left behind in homes that were used as Nazi bases. I haven’t encountered any machine that came to the market in any other way.

When did Enigma machines start arriving on the auction market? Probably the late 1990s or early 2000s. They were previously placed in scientific instrument sales or World War II sales. Those buyers looked at them more as relics. They put them on a shelf, and they wouldn’t be touched. They were part of history. The biggest leap in prices was in 2015, when I was at Bonhams. The sale with the Alan Turing manuscript also had an Enigma machine, and I want to say it made $269,000. It was a record price and a big leap for a three-rotor. It was fully operational.

How did the 2015 Bonhams sale of the three-rotor Enigma machine change things? It was a big shift. They were no longer World War II relics sitting on a shelf. Now they were objects from the history of computing that you could play with. Interest in Alan Turing’s manuscript came from the tech world. The shift in interest in the machines went from World War II to tech–a different client base. That’s when things took off, I think. Christie’s sold a four-rotor Enigma machine in 2017 for $547,500, which was a new world record. The one we sold in December was way above that.

Why did the four-rotor Enigma machine that Sotheby’s sold in December 2019 do so much better than any other offered at auction? It had a combination of everything you want. This machine had fantastic condition and a really killer history. It’s the only one I’ve seen or know of with an unbroken chain of provenance. Condition plus provenance plus rarity is where you find higher prices. Buyers understood it was a trifecta.

How often do three-rotor Enigma machines come to auction, and how often do four-rotor Enigma machines come up? The E1 [the three-rotor], once or twice a year, maybe. A really, really good one comes up every other year. I could probably sell many E1s every year but they wouldn’t be in great condition, or wouldn’t have a great provenance, or they wouldn’t function. The M4 [four-rotor], there have been four I’m aware of in the past six years. Two have been at Sotheby’s since I’ve been here. One was at Christie’s, and one was at Bonhams. I always look for four-rotors. I know where to find three-rotors. It’s not difficult to acquire one. Getting an M4 is a different story, much more difficult to do.

How many Enigma machines have you personally handled? Quite a few. I’d say at least one dozen, if not more. I’m including ones that clients own but need to figure out if it’s working or not.

Do Enigma machines have to work to have value to collectors? They definitely wouldn’t be worthless, but there would be less interest in it. I’ve previously seen them come up in World War II and scientific instrument sales not working and they were still sold. I have seen machines missing most of their hardware still sell. But I’ll see a higher price for an operational machine.

Why do functional Enigma machines command higher prices? A functional Enigma machine is a totally different thing. It becomes an interactive piece that can encode messages, and you can show people how to decode messages. They come into the gallery and I ask, “You want to see how this thing works?” The looks on peoples’ faces… going from a box on a shelf to showing them how it works, it blows peoples’ minds every time. If the choice is between a machine that blows peoples’ minds versus a box sitting on a shelf, you’re going to go for this machine.

How easy or difficult is it to operate a four-rotor Enigma machine? It seems easy to me because I’ve played with the machines for a long time. They’re not difficult to operate. They’re actually pretty clean and elegant. I understand the math behind it is more difficult.

Do Enigma machines make any noise? What do they sound like? They make a very satisfying kind of thunk sound, very similar to old typewriters, but very distinctive. It’s louder than an old typewriter. You couldn’t use it in secret.

That’s why you need a bunker… Yes! [Laughs]

What is the four-rotor Enigma machine like in person? I think it’s very difficult to understand what these machines really are just with a camera. You need to put your hands on them and play with them. I love Enigma machines. I’m obsessed with them. If I could have two M4s and two E1s, I’d be very happy and very broke. If you can forget about what they were used for, they’re amazing technical marvels. It’s impossible to convey in a video. The experience is a different thing. And it’s heavy. It takes a strong person to lug it around.

Do you know how much it weighs? I think the E1 and the M4 are about the same weight. This is a two-arm job. It comes with a leather strap, but there’s no way I’d try to carry it with a leather strap.

In what ways does the four-rotor Enigma machine bring pleasure to someone who loves all things analog? Opening the machine up and seeing the guts, seeing how the rotors are put together, how it’s engineered to fit together, nest together, it’s so satisfying. I’m a person who likes to look under the hoods of cars. I like taking things apart and putting them back together. If you’re that person, an Enigma machine is so fun.

What was your role in the auction? Were you on the phone? Yes.

With the winner? Yes.

Did you have a notion that the four-rotor Enigma machine might break the world auction record? I always hoped for that. I didn’t think it was unreasonable. I think it was a fair price, and it was right for it to sell for that price. The provenance and the condition were beyond the others [that have been] at auction. I thought it should, at minimum, sell for the high estimate. I was happy with where the sale ended up.

What role did the provenance play in driving it toward the record price? I think it played a big role. It really did. People were excited about the story. If you take the provenance away, it gets closer to the high estimate.

And its condition, what role did that play in the record price? The machine was issued with, I believe, seven rotors. Each rotor has a serial number. One way to determine if a machine was used during wartime is if the serial number of the rotors match the serial number of the machine. The serial numbers on the rotors do not match the machine–that means it was used. When it sat in a bunker, all the rotors were piled on a table, because they were interchangeable in terms of wiring. You could use an R7 [a seventh rotor] in any machine. When the machine was taken, it had a full complement of rotors and [the original private owner] grabbed a box with extra rotors. The rotors in the box had different serial numbers than the machine, which is totally fine. If they matched, that means the machine was never used, or used in isolation.

So the world of Enigma machines is not at all like the world of classic cars, where you want the number on the engine to match the number on the chassis. Exactly.

What do you think it would take for an Enigma machine to cross the seven-figure threshold? Would this particular one have to return to auction? I think it’s definitely possible. It’s hard to say what kind of machine would do that. It’d have to be a famous machine with some sort of super-celebrity provenance to it, like Admiral Doenitz’s own.

Does Admiral Doenitz’s four-rotor Enigma machine still exist? I don’t know, but I can’t wait to find out!

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Cassandra Hatton has appeared on The Hot Bid before, talking about a group of Apollo 11 moon walk videotape recordings, Richard Feynman’s Nobel Prize, and an Apollo 13 flight plan

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