The “Enigma” cipher machine is often portrayed as the Third Reich’s “Koschei’s needle,” which British naval personnel managed to steal, subsequently allowing British mathematicians to unravel its secrets. The Germans realized their messages were being read far too late, but imagine their surprise had they known that neither British science nor the genius of Alan Turing was even necessary for this feat. Long before Turing, the secret of the “Enigma” was cracked, and not by the British.
The Puzzle
During the First World War, Germany faced an insurmountable issue. Communication with the fleet or foreign embassies was restricted to radio, a medium anyone could intercept. The Germans dispatched orders and messages in encrypted form, but their cipher was exceedingly basic. British intelligence decrypted virtually 100% of German radio traffic, which consistently resulted in both tactical outcomes, such as the destruction of submarines and ships, and strategic ones—an intercepted German message to the ambassador in Washington pushed the United States to enter the war.
Reflecting on this experience after their defeat, and recognizing that communication would play an even more critical role in the strategy of Blitzkrieg in a future conflict, the Germans sought a permanent solution to the eavesdropping problem. They turned their attention to the invention of engineer Arthur Scherbius—a portable device marketed as “Enigma,” which enabled the automated, continuous encryption of messages using a highly complex (for that era) code.
A dramatic legend is associated with the “Enigma’s” impact on the course of World War II. The machine supposedly rendered German communications impenetrable, allowing for the secret planning of offensives or the coordination of submarine operations. This held true until the brilliant British mathematician Alan Turing constructed the Bombe calculating machine, one of the ancestors of modern computers. Yet, even Turing’s genius would have been ineffective had the heroic sailors of the Royal Navy not managed to capture an “Enigma” unit.
British fleet captures U-110 / Bundesarchiv
In the early morning of May 9, 1941, off the coast of Greenland, the large German ocean-going submarine U-110 (Type IXB) initiated an attack on British convoy OB 318. Its captain, Fritz-Julius Lemp, succeeded in slipping past the escort vessels and sank two cargo ships with torpedoes. As he prepared to attack a third vessel, the British corvette Aubrietia spotted its periscope protruding from the water. It attained a sonar lock on the submarine and, along with other escort ships, began dropping depth charges. The explosions severely damaged U-110, forcing Lemp to choose between an emergency surface or sinking to the bottom.
The boat surfaced, and the destroyer Broadway headed for a ramming maneuver, but at the last moment, it changed its decision and dropped a few more bombs to increase pressure on the crew. Lemp saw the boat sinking and gave the order: “Final, everyone out.” The sailors rushed out, came under fire from the British vessels, and jumped overboard.
Once in the water, Lemp realized the boat was actually remaining afloat and that the codebooks and a fully functional “Enigma” remained on board. Submarine command was generally permissive regarding surrender under duress, but destroying secret equipment was mandated at all costs, even life. The captain scrambled back toward the boat, and he was never seen again. The sailors believed a British sailor had shot him in the water, and soon afterwards, a boarding party from the destroyer Bulldog, led by Sub-Lieutenant David Balme, prepared to board the damaged submarine.
To enter the possibly mined vessel, one had to descend a vertical shaft using both hands—rendering oneself completely defenseless. Balme went down in history as a hero, but according to him, his primary emotion upon entering U-110 was fear. “Going down those ladders and thinking there could be Germans up there ready to shoot you… it was terrifying. We couldn’t believe they had just abandoned the U-boat. That haunted me for 15 or 20 years afterward,” he recalled.
One model of the “Enigma” / Leonardo da Vinci National Museum of Science and Technology
However, there were no mines or ambushes, and the British seized everything they could carry, including the “Enigma” machine and the cipher books. Following this, U-110 was sunk during towing back to Britain to maintain secrecy, and all operation participants received orders never to disclose the events under any circumstances.
The “Enigma” was transported to the secret facility at Bletchley Park, where British cryptanalysts examined its design, identified vulnerabilities, and developed a mechanism for breaking its codes.
The capture of U-110 was crucial for cracking German codes, but the dramatic story above represents only part of the truth, significantly exaggerating the German evil genius, whose undoing required nothing short of a miracle.
How “Enigma” Worked
First and foremost, the mystique surrounding the “Enigma” must be dispelled. It is not a mystical black box but, in a sense, a very sophisticated arithmetic machine executing a straightforward algorithm.
Any person, even a child, can encode messages using a substitution alphabet—agreeing with a friend to replace “M” with “Щ” and “D” with “У,” and so on. Such a cipher is called a monoalphabetic cipher and is very easy to crack by identifying the most frequently used letters in the ciphertext and matching them to the most common letters in the language—in Russian, these are “О,” “Е,” and “А.”
This vulnerability can be countered using a polyalphabetic cipher: employing one substitution dictionary for the first letter in the text, another for the second, a third for the third, and so on. Eventually, after a certain number of symbols, the cycle would close, and the sequence of substitution schemes would begin to repeat. The greater the number of substitution schemes used and the more nuances they contain, the more secure the code. However, in practice, manually managing complex polyalphabetic ciphers suitable for serial application is impossible, as encrypting a simple message would take an entire day, and the instructions for their use would resemble a massive tome.
The rotors of the “Enigma” /
This is where “Enigma” provided assistance by automating the process. The machine featured a keyboard, illuminated letter indicators serving as a “monitor,” and a set of rotating rotors, much like those in a combination lock. The rotors were electrically interconnected, and when an operator pressed a key, the machine replaced it with another, encrypted one, depending on the rotors’ current positions, and lit it up. Simultaneously, pressing a key caused the outermost rotor to advance by one position, altering the electrical wiring configuration and, consequently, the substitution alphabet. After the outermost rotor completed a full rotation, the next one advanced by one step, and so on down the line.
Three-rotor machines offered 17,576 substitution configurations, meaning that within a single text, this sequence would never repeat.
Four rotors increased this number to 456,976, and by altering the wiring connections within the machine using a plugboard, the Germans elevated the number of possible alphabets to hundreds of trillions.
French cryptanalysts, after receiving materials on the “Enigma’s” construction from their spy Hans-Thilo Schmidt in 1932, concluded that breaking this code was impossible. Just in case, they shared the materials with their Polish allies and promptly forgot about them—a decision they would regret.
Polish Science
In Poland, the analysis of intercepted messages was undertaken starting in the autumn of 1932 by 27-year-old mathematician Marian Rejewski. Within a few weeks, he discovered that the initial steps to break the “Enigma” required no knowledge of its internal workings because the Germans had made a critical error in their operational procedure.
Marian Rejewski Monument / Michał Kubiak/Wikimedia Commons
The cryptographers had a set “daily key” that determined the initial rotor positions—for example, “UXN.” Following this, they had to devise a specific message key (e.g., “QMY”) and type it twice at the start of the message, using the “UXN” key, resulting in something like “TNI QSH.” The rest of the message was then encoded after setting the rotors to the “QMY” key. The three-digit key was intended to be decrypted by the receiving operator using the “daily key,” after which they would switch the machine to decrypt using the “QMY” key. The double repetition of the three-digit key was for redundancy, but this became a catastrophic vulnerability. Rejewski realized that the first three letters of the message were identical to the second three letters (meaning TNI and QSH looked identical in their initial form). Furthermore, before the war, German cryptographers were often lazy and used message keys like “AAA” or “BBB”—this was far worse for information security than if they had stuck the daily key onto the machine with a sticker.
By analyzing a large volume of messages, receiving the materials passed on by the French from Schmidt, and solving a series of equations, Rejewski was able to analytically reconstruct the “Enigma’s” internal structure and build a replica. This was followed by the development of a method for calculating specific keys, leading, by the mid-1930s, to the decryption of complete messages.
The Germans continuously updated the “Enigma” and its operational procedures, making message decryption increasingly difficult. Nevertheless, it was Rejewski’s groundwork that formed the basis for the British efforts to decrypt it: shortly before the war began, the Poles transmitted everything they knew, including a replica of the machine, to the British.
An “Enigma” clone created by Polish cryptanalysts after their flight to France / Pilsudski Institute London
Alan Turing’s merit consisted solely of putting the decryption effort onto a production line, automating it, and learning to rapidly adapt to any machine improvements.
Therefore, the capture of the U-110 cipher equipment was undoubtedly an important event, but it was not akin to stealing Koschei’s needle. The Poles had managed to create an unauthorized copy much earlier.
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