Enigma: How Polish Mathematicians Cracked the German Code

The Germans were convinced that their cipher machine Enigma was unbreakable. The number of possible settings exceeded imagination, and the keys were changed daily. Yet, as early as the turn of 1932 and 1933, German messages were being read in Warsaw. This was accomplished by three young mathematicians from Poznań: Marian Rejewski, Jerzy Różycki, and Henryk Zygalski, who worked for the Cipher Bureau of the General Staff.

In this guide, we recount the entire story: how Enigma worked, why the idea arose to have mathematicians break the codes instead of linguists, how Rejewski reconstructed the interior of a machine he had never seen, the methods the Poles used to read Enigma until 1939, and what they conveyed to the British and French in the forest near Warsaw just before the war. We then follow the fates of the cryptologists during and after the war, the work at Bletchley Park, and how the secret only came to light thirty years later.

How Enigma Worked

From the outside, Enigma looked unremarkable: a wooden box with a keyboard like a typewriter, above it a panel with round windows where letters lit up. It printed nothing. The cipher operator pressed a key, and a different letter lit up on the panel. Subsequent letters had to be written down manually, and the completed string of characters was sent by the telegraph operator using Morse code. The recipient, who set their machine the same way, entered the ciphertext, and the plaintext lit up on their panel. Thus, the same machine and the same settings were used for both encryption and decryption.

Keyboard, Lights, and Rotors

The military Enigma had 26 keys for the Latin alphabet letters and the same number of lights. Between the key and the light, the current passed through the heart of the machine, the rotors (ciphering drums). Each rotor was a disk with 26 contacts on one side and 26 on the other, connected in the middle by a tangle of wires. The contact “A” on the left could be connected, for example, to contact “K” on the right. In the version used by the army and air force, three rotors were placed next to each other in the machine, while the navy eventually used more.

The crucial aspect was that the rotors rotated. After each key press, the right rotor moved one position, and periodically, like in a mileage counter, it pulled the adjacent one along. Therefore, the same letter entered twice in a row produced two different letters in the ciphertext. The cipher changed with each character, which negated classical counting methods for determining which letter appeared most frequently in the text.

Reversing Drum, or Why a Letter Never Transforms into Itself

After passing through the three rotors, the current reached the reversing drum (reflector). This stationary element connected contacts in pairs and sent the signal back through all three rotors, but via a different path. This made the machine symmetrical: if, under a given setting, A became P, then P became A. This symmetry allowed the same machine to be used for both encryption and decryption.

However, this convenient symmetry had a hidden cost. Since the reflector always pairs letters, no letter could be encrypted into itself. A never became A, and B never became B. The designers considered this an advantage, but in practice, it turned out to be a serious cryptographic weakness, as it allowed entire groups of possible solutions to be eliminated. Both the Poles and the British later exploited this feature.

Plugboard

The military version had one more element not found in commercial machines: the plugboard, located at the front of the box under the keyboard. It resembled a small telephone exchange. With a cable and two plugs, two letters were connected, for example, E with Q, and from that moment on, they swapped places before the current reached the rotors and again on the way back to the lights. Up to 13 pairs of letters could be connected on the plugboard. In the early period, when the Poles began their work, the Germans used six cables, meaning they swapped six pairs, while the remaining 14 letters remained unchanged. This number began to change in 1936.

Daily Key and Message Key

For two Enigmas to “communicate” with each other, they had to be set identically. This was facilitated by key tables sent to units, usually with settings valid for one day. The daily key specified which rotors to insert and in what order, how to adjust the rings with letters on the rotors, which letters to connect with cables on the plugboard, and in what initial position to set the rotors. This last setting, known in German as Grundstellung, was common for all messages in a given network throughout the day until September 1938. The order of the rotors was initially changed only once a quarter, from February 1936 monthly, and from November 1936 daily.

Encrypting all messages of the day with the same setting would be too risky, so each message received its own message key. The cipher operator invented three letters, for example, EIN, set the rotors to the daily position, and entered their three letters twice: EINEIN. The six encrypted characters were placed at the beginning of the message. Then, they adjusted the rotors to EIN and encrypted the actual content. This duplication was meant to protect against errors in reception, as the radio was crackling, and a mistake in the key meant that the entire message could not be read.

This duplication turned out to be the greatest weakness of the entire system. The first and fourth letters of each message were the cipher of the same letter, as were the second and fifth, and the third and sixth. With dozens of messages from one day, a mathematician could read the regularities encoded in the machine's structure from these pairs. How Marian Rejewski did this will be explained later in the article. The army and air force only abandoned the double entry of the key in 1940.

How Many Possible Settings There Were

The number of combinations is impressive even today. For the military Enigma, in which three rotors were chosen from a set of five, and ten pairs of letters were connected on the plugboard, the English Wikipedia states there are 158,962,555,217,826,360,000 possible settings, or nearly 159 trillion. This number is the product of 60 possible sets and orders of rotors, 17,576 initial positions (26 × 26 × 26), and about 150.7 trillion plugboard connections. In 1932, with three rotors and six cables, the number of combinations was lower, but still so high that checking them one by one was out of the question. The Polish Wikipedia notes one more thing: if the internal connections of the rotors are not known, as was the case at the beginning, the number of possibilities rises to the order of 10 to the power of 114. Therefore, the Germans considered Enigma practically unbreakable.

The Inventor and the Path to the Military

The father of Enigma was the German engineer Arthur Scherbius. On February 23, 1918, he filed a patent application for a cipher machine with rotating rotors and, together with Richard Ritter, founded the company Scherbius und Ritter. Neither the navy nor the German foreign ministry were interested at that time. On July 9, 1923, the company Chiffriermaschinen AG was established, which began selling Enigma as a device for banks and companies wanting to protect trade secrets.

The first models, showcased at the World Postal Union Congress in 1924, were large and heavy, had a built-in typewriter, and did not yet have a reflector. Later, the typewriter was replaced by a panel with lights, and a reflector appeared, the idea of which is attributed to Willi Korn. Sources describe the sequence and designations of these early models differently. It is certain that the reflector was present in model C from 1926, and in 1927 it was replaced by model D, which was also sold abroad.

The military quickly appreciated the invention. The German navy introduced its own version of Enigma in 1926. The Reichswehr, the army of the Weimar Republic, adopted the Enigma G model on July 15, 1928. In 1930, it was modified into Enigma I, whose most important novelty was the plugboard. From then on, the commercial and military Enigma were essentially different machines: the military version had a plugboard and different connections in the rotors. Therefore, anyone who bought a commercial version did not have the key to military messages, only a manual on how it worked.

How It All Began

Polish cryptology did not start with Enigma. It began with the war against the Bolsheviks, when decoding the opponent's messages could determine the fate of the state.

Lieutenant Kowalewski and the 1920 War

In August 1919, Lieutenant Jan Kowalewski, born in 1892 in Łódź, joined the Cipher Section of the II Department of the General Staff. Initially, he sorted intercepted telegrams. According to accounts cited in his biography, while substituting for a colleague on leave, out of boredom, he took a Soviet message and slid a comb with broken teeth over the text to catch repeating sequences of characters. He knew the method from Edgar Allan Poe's story “The Gold-Bug.” At the turn of August and September 1919, he broke the first keys of the Red Army.

Kowalewski involved outstanding mathematicians in his work: Stefan Mazurkiewicz, Wacław Sierpiński, and Stanisław Leśniewski. Between 1919 and 1921, Polish cryptologists broke about one hundred Russian ciphers. In July 1920 alone, 410 messages from Soviet commanders, including Tukhachevsky and Trotsky, were decoded. Tukhachevsky's order to Budyonny was intercepted on August 19, 1920, and decoded the next day. Kowalewski's reports are credited with having a significant impact on Józef Piłsudski's decisions during the Battle of Warsaw. For this work, he received the Silver Cross of Virtuti Militari.

Cipher Bureau

The Cipher Section, established on May 8, 1919, by Lieutenant Józef Serafin Stanslicki, underwent several reorganizations. In mid-1931, the Cipher Bureau of the II Department was formed from the merger of the Radio Intelligence Section and the Own Cipher Section. It was located in the Saski Palace in Warsaw, in the building of the General Staff. The German Section, designated BS-4, worked there until 1937, when it moved to a specially built center in the Kabacki Forest near Pyry.

The Year 1928: Messages That Could Not Be Read

In the first years after the war, Polish radio intelligence managed to handle German manual ciphers. However, on July 15, 1928, German military radio stations began transmitting messages encrypted by machine. Polish stations intercepted them, but attempts to decode them yielded no results and were eventually abandoned. Statistical analysis only allowed for the conclusion that the Germans were using machine ciphers. For a country situated between Germany and the Soviet Union, the loss of insight into the communication of its western neighbor was a serious problem.

A Package at the Warsaw Customs

This period is associated with an anecdote described by Marian Rejewski himself. At the end of 1927 or the beginning of 1928, a shipment was supposed to arrive at the customs office in Warsaw from Germany, declared as radio equipment. A representative of the German company insisted that it be returned before clearance, as it had been sent by mistake. This nervousness alarmed the customs officers, who notified the military. It was a Saturday afternoon, so the specialists had time to calmly inspect the contents. Instead of a radio, they found a cipher machine in the crate. They examined it and carefully repacked it.

The story is colorful, but it should not be overestimated. Rejewski suspected that it was an ordinary commercial Enigma, as the military version did not exist at that time. The Polish Wikipedia emphasizes that this episode had virtually no significance for breaking the cipher, only helping to date the beginning of interest in Enigma. Sources even disagree on the date: some calendars move this event to 1929 and to the Okęcie airport.

Commercial Enigma on the Desk

More important was that the Cipher Bureau legally acquired a civilian version of the Enigma. According to the Intelligence Agency, it was purchased by engineer Antoni Palluth, associated with the German section, and the calendar of the portal dzieje.pl dates the purchase to 1932. The commercial machine allowed for an understanding of the principles of the rotors and reflector. However, it was not sufficient for reading military messages, as these were encrypted by a machine with a plugboard and other internal connections in the rotors.

Secret Course in Poznań

In the Bureau, it was recognized that breaking the machine cipher required not linguists, but mathematicians, and those who were proficient in German. The natural place for searching was the University of Poznań: Greater Poland had been part of Prussia just a decade earlier, and many students attended German schools. In the early days of 1929, Professor Zdzisław Krygowski, head of mathematics at the Faculty of Mathematics and Natural Sciences, received a letter from Warsaw. He was asked to identify outstanding third and fourth-year students who knew German and to help organize a course.

A few days later, Major Franciszek Pokorny, head of Polish radio intelligence, and Lieutenant Maksymilian Ciężki arrived in Poznań, dressed in civilian clothes. Civil engineer Antoni Palluth also lectured. Twenty-three people were accepted into the course. Classes took place from January 15 to March 22, 1929, twice a week, in the evenings. The course was secret. The program, as Rejewski later established, was based on the textbook by French General Marcel Givierge, “Cours de cryptographie,” published in 1925. According to the portal dzieje.pl, 20 students completed the course, and only five received a good or very good grade.

Among the graduates, Ciężki identified the three most talented: Marian Rejewski, Jerzy Różycki, and Henryk Zygalski. Piotr Bojarski, the head of the Enigma Cipher Center, recalls that there was at least one woman in the course, although history remembers only the three men.

Branch at Święty Marcin

After the course, the Cipher Bureau established a branch in Poznań, where the best graduates, still students, broke intercepted German messages. They worked in the building of the Prussian military supply office on Święty Marcin Street, in the basement, part-time. Rejewski and Zygalski worked there about 12 hours a week. Różycki dealt, among other things, with the four-letter code of the German navy. The original building, severely damaged, was demolished after the war. On the same site, in the Collegium Martineum building at Święty Marcin 78, the Enigma Cipher Center operates today. “Here, where we are, the cryptologists Różycki, Zygalski, and Rejewski worked,” Piotr Bojarski told PAP.

To Warsaw, to the Saski Palace

In the summer of 1932, the Poznań branch was closed. The three mathematicians were transferred to Warsaw and, from September 1, 1932, worked in the Cipher Bureau as civilian employees in the Saski Palace, the seat of the General Staff. They were then aged between 23 and 27. At the end of 1932, Ciężki assigned Rejewski to work on Enigma. This marked the beginning of a story that would have significant consequences for the course of the war a few years later.

Marian Rejewski, Jerzy Różycki, Henryk Zygalski – who were they

Three young men from Poznań were connected by their university, Professor Krygowski, and their knowledge of German. However, they came from very different worlds: from Bydgoszcz, from Ukraine, and from a tailoring workshop in Poznań.

Marian Rejewski (1905–1980)

Marian Rejewski was born on August 16, 1905, in Bydgoszcz, then Prussian Bromberg. He was the son of Józef, a merchant dealing in tobacco, and Matylda née Thoms. The family first lived at 6 Wileńska Street, then moved to a house with a garden at 6a Zduny Street. Marian attended the classical gymnasium in Bydgoszcz, which was German-speaking during Prussian times, and graduated in 1923.

At the University of Poznań, he studied mathematics. On March 1, 1929, he obtained a Master of Philosophy degree in mathematics based on a thesis on doubly periodic functions, with a very good grade. He was directed to a cryptology course by Professor Krygowski. Sources differ on whether Rejewski completed the course: according to dzieje.pl, he did not finish it because he went to study in Germany.

A few weeks after graduation, he went to Göttingen for a two-year study of mathematical and insurance statistics. He did not complete these studies. In the summer of 1930, while at home, he accepted an offer for a mathematics assistantship at the University of Poznań and simultaneously began working at the Poznań branch of the Cipher Bureau. He was described as a short, modest, and thoughtful young man. The Intelligence Agency quotes a description from friends: "a shy bespectacled man." In 1932, he moved to Warsaw, and on June 20, 1934, he married Irena Maria Lewandowska.

Jerzy Różycki (1909–1942)

The youngest of the trio, Jerzy Witold Różycki, was born on July 24, 1909, in Olszany in present-day Ukraine, then part of the Russian Empire. He was the fourth and youngest child of Zygmunt Różycki, a pharmacist and a graduate of the University of St. Petersburg, and Wanda née Benit. He spent his early years in Ukraine and studied in Kyiv. In 1918, the family fled to Poland and settled in Wyszków on the Bug River, where his father ran pharmacies in Wyszków and nearby Długosiodło.

In May 1926, Jerzy graduated from a coeducational gymnasium in Wyszków. He chose to study at the Faculty of Mathematical and Natural Sciences in Poznań, even though he was not from Greater Poland, and additionally studied German. He belonged to the academic corporation Chrobria. As a student, he was qualified for the cryptology course and worked at the Poznań branch of the Cipher Bureau even before graduating. He obtained his Master's degree in mathematics in February 1932, and in December 1937, a second degree in geography. In July 1938, he married Maria Barbara Majka, and in May 1939, they had a son, Janusz.

Henryk Zygalski (1908–1978)

Henryk Zygalski was the only native of Poznań among this group. He was born on July 15, 1908, in Poznań, then Prussian Posen. His father Michał, a tailor, came from the Wolsztyn area, and his mother Stanisława née Kielisz. His parents ran a tailoring workshop on the ground floor of a tenement house on Mielżyńskiego Street, where the family lived. Henryk had a younger sister, Monika, born in 1910.

At the age of seven, he went to a German school on Mielżyńskiego Street, and then studied for nine years at the St. Mary Magdalene Gymnasium. He particularly enjoyed mathematics and physics. In May 1926, he graduated with a very good grade in mathematics, and in the fall, he began studies at the Faculty of Mathematical and Natural Sciences, which was then located in the former Imperial Castle. His main teacher was Professor Krygowski.

As a third-year student, he was on the list of candidates for the cryptology course. After the course, he worked at the Cipher Bureau branch while continuing his studies. He defended his Master's thesis on the delimitation of roots of numerical equations with a very good grade, before a committee chaired by Krygowski. In 1932, he moved to Warsaw with his colleagues to the Cipher Bureau in the Saski Palace.

Thus, in 1932, three mathematicians under thirty met in one room: the son of a Bydgoszcz merchant, the son of a pharmacist from Ukraine, and the son of a Poznań tailor. None of them were professional soldiers. All three had taken German lessons and attended lectures by Professor Krygowski, and before them was a machine that its creators believed to be unbreakable.

The breakthrough of December 1932 – how Rejewski reconstructed the interior of the Enigma

In the autumn of 1932 – according to the most frequently cited version, at the end of October or the beginning of November – Captain Maksymilian Ciężki, head of the German section of the Cipher Bureau, assigned Marian Rejewski a task that even his closest colleagues were unaware of. Rejewski was to spend several hours a day working on the military Enigma. The Bureau had a commercial version of the machine that could be purchased on the market, but the military version differed from it in internal wiring. And it was precisely the wiring of the rotors that was the greatest mystery.

The task seemed hopeless. The intercepted messages were strings of seemingly random letters, and the machine that produced them had three rotors with unknown connections, an unknown reversing drum, and a connector that additionally swapped letter pairs. Where previous codebreakers looked for repeated words and lucky hits, Rejewski reached for a tool from university mathematics – the theory of permutations, a branch of algebra describing the rearrangement of elements of a set.

Weak point: the key assigned twice

The German procedure had one feature that proved to be fatal. Each cipher clerk set their own three-letter message key before the actual message and encrypted it twice, just in case the radio distorted the character. Therefore, at the beginning of each message, there appeared six letters, where the first and fourth, the second and fifth, and the third and sixth were encryptions of the same plaintext letter, only in positions of the machine spaced three steps apart.

Rejewski collected messages from one day, sent with the same initial setting, and arranged them into tables: if in one message A was in the first position and D in the fourth, he recorded that A "transforms" into D. After several dozen messages, such transformations formed closed loops – cycles. One can imagine this like a game of chain: from A we go to D, from D to K, from K back to A, and the loop closes. Each day had its own set of such loops of specific lengths, which Rejewski called the characteristic.

The most important discovery was this: the connector changed which letters were in the loops, but did not change their number or length. Therefore, the characteristic of the day depended solely on the arrangement of the rotors, not on the wires that the Germans reconnected daily. This observation would later become the basis for the catalog of cards. In reconstructing the interior of the machine, Rejewski derived six permutations from the six letters of the indicator and a system of equations describing the interior of the machine. The problem was that there were still too many unknowns for these equations to be solved.

A package from the French

Help came from Paris. Soon after the introduction of the military Enigma, Hans-Thilo Schmidt, an official of the German military Cipher Bureau (Chiffrierstelle), offered his services to French intelligence, having obtained the position there through the influence of his brother Rudolf. The French gave him the codename "Asché," and the contact with him was maintained by an agent known as "Rex," or Rodolphe Lemoine. Schmidt sold copies of the Enigma operating instructions, rules for using it, and lists of key settings. These materials reached Captain Gustave Bertrand, head of the French cryptology section, who in December 1932 passed them on to Major Gwidon Langer, head of the Polish Cipher Bureau.

Rejewski received the documents around December 9 or 10, 1932. He later recalled that Bertrand brought the materials to Warsaw on December 8, and this same date is given by the Polish Intelligence Agency. The most valuable were the key settings for September and October 1932. Knowing the key of the day, Rejewski could "extract" the function of the connector from the equations and reduce the number of unknowns to a manageable level for mathematics.

Even then, something was not right. The equations yielded contradictory results until Rejewski questioned one assumption. In the commercial Enigma, the keys connected to the input drum in the order of the typewriter keyboard. Rejewski guessed that in the military version, the connections ran simply alphabetically: A to the first contact, B to the second, and so on. He was correct. A helpful example from the German instructions provided plaintext, its encrypted form, and the key – allowing verification that the reconstructed machine encrypted exactly like the original. By the end of 1932, Rejewski knew the wiring of all three rotors and the reversing drum.

How much the French documents helped and how much was due to Rejewski's independent mathematics is a question historians still ask today. American cryptology historian David Kahn called the solution "an astounding achievement" of Rejewski himself. At the same time, Schmidt's materials are considered practically key, for without them the equations would have remained unsolvable. Both things are true at once: the spy provided the keys, but no one other than the Poles could use them to reconstruct the interior of the machine. The fate of Schmidt himself ended tragically. Exposed by Lemoine, who fell into the hands of the Gestapo after France's defeat, he was arrested on April 1, 1943, and died on September 19, 1943, in Berlin. Whether he was executed or took his own life – sources differ.

The first read messages

According to accounts cited by Polish historians, Rejewski likely read the first message on the last day of 1932. The date December 31, 1932, is also given by the Intelligence Agency as the moment of the first reading of the ciphered messages. At the turn of 1932 and 1933, Jerzy Różycki and Henryk Zygalski, Rejewski's colleagues from the Poznań cryptology course, joined the work on the Enigma. Rejewski did not receive any further sets of keys from the French – the team had to devise methods that would allow them to reconstruct the daily keys without the help of the spy.

Polish duplicates from AVA

Knowledge of the wiring alone was not enough. Machines were needed to read the messages. They were built by the Warsaw Radio Engineering Factory AVA, founded by Antoni Palluth, Edward Fokczyński, and brothers Ludomir and Leonard Danilewicz. The name came from the combination of Palluth's (TPVA) and the Danilewicz brothers' (TPAV) amateur radio call signs. Palluth, an engineer and also a collaborator of the Cipher Bureau, was one of its four directors.

As early as January 1933, AVA produced the first "duplicate" of the military Enigma, and by mid-1934, several dozen copies. The Intelligence Agency mentions several copies that the Cipher Bureau was already using in 1934. The same factories later built the cyclometer and cryptological bombs.

How the Poles read the Enigma 1933–1939

Breaking the Enigma was not a one-time feat but the beginning of a six-year race. Every day, the Germans changed the key: the order of the rotors, their initial setting, and the connections of the connector. Therefore, the Poles had to reconstruct new settings daily, while the Germans periodically complicated the procedures. Each change required a new method or a new device.

The grid, cyclometer, and card catalog

The first method was the grid. It utilized the fact that the connector only swapped six pairs of letters at that time, leaving fourteen letters unchanged. The cryptologists compared the recorded permutations with the successive possible positions of the rotor and looked for one where everything matched. This method allowed for determining the right rotor and even the connections of the connector, but it was tedious, manual, and dependent on how many letters remained unchanged.

Therefore, Rejewski invented the cyclometer – a device that showed what characteristic, or what arrangement of loops, the machine produced for each possible setting. The dates of its creation differ in sources: 1934 or 1935 is most often cited, while the Intelligence Agency also mentions 1936. Using the cyclometer, the team compiled a card catalog: for 17,576 rotor settings and six possible orders of three rotors, this resulted in 105,456 entries. Preparing the catalog took over a year, but then finding the key of the day took only 12–20 minutes. It was enough to determine the characteristic from the morning messages and find it in the card catalog.

Różycki's clock method

Jerzy Różycki developed the so-called clock method. It allowed in some cases to determine which rotor was on the right side, meaning which one rotated with each key press. This seemingly minor information narrowed down the number of possibilities that needed to be checked. Since the Cipher Bureau's archives were deliberately destroyed during the evacuation in September 1939, it is difficult to determine Różycki's personal contribution to the daily reconstruction of keys. It is known, however, that his idea survived the war: by the end of 1939, Alan Turing developed the clock method into a technique called "Banburismus" at Bletchley Park.

The Germans tighten the screws

Changes came in waves. The order of the rotors, initially changed quarterly, then monthly, eventually began to change daily. From October 1, 1936, the connector no longer had a fixed six pairs, but from five to eight connections, which significantly weakened the grid. On May 1, 1937, the navy introduced a new key procedure, and the characteristic method ceased to work for naval messages. On November 1 or 2, 1937, the Germans replaced the reversing drum – the entire catalog had to be recalculated from scratch. Nevertheless, as stated in Rejewski's biography on the MacTutor website of St. Andrews University, by January 1938, the team was reading about three-quarters of the messages transmitted to them.

The real blow came on September 15, 1938. From that day on, the cipher clerks of the land and air forces chose their initial settings from which they encrypted the message key. All messages from a given day ceased to have a common starting point, and the characteristics – and the entire card catalog – lost their meaning. They had to start over.

Zygalski's sheets

The response from Henryk Zygalski, developed around October 1938, was the perforated sheets, later named Zygalski's sheets. They utilized the so-called female situations – instances where the same letter of the key was encrypted twice into the same letter, e.g., when in a six-letter indicator the first and fourth letters were identical. This occurred in about one out of every eight messages.

For each rotor arrangement, there was a set of 26 sheets, one for each position of the left rotor. Each sheet was a grid of 26 by 26 fields, repeated vertically and horizontally, with holes in places where a female situation could occur. The cryptologists overlaid the sheets with the appropriate offset and looked for places where the holes aligned across all layers. To succeed, about ten females from one day were needed. The great advantage of the method was its independence from the number of connections of the connector. The downside was the manual labor: the Poles cut thousands of holes with razor blades, which took a very long time. The British later did this mechanically.

The cryptological bomb

Around the same time, in the autumn of 1938, Rejewski designed the cryptological bomb. It was an electrically driven combination of six Enigmas that automatically cycled through the rotor settings and stopped when it hit a configuration that matched the females. The bomb needed only three females instead of about ten and reduced the determination of the key to about two hours. AVA built six such devices, one for each of the six possible rotor orders at that time. They were ready by mid-November 1938.

It is worth avoiding a common simplification here. The Polish bomb and the British Turing bomb are two different devices. The Polish machine was based on the doubly encrypted key and females. Turing, using Polish experiences, designed a machine in the autumn of 1939 that operated on a different principle (the first unit was launched at Bletchley Park in March 1940) – it searched for settings that matched a guessed fragment of plaintext, the so-called "crib." It did not depend on the doubly encrypted key.

December 1938: five rotors instead of three

On December 15, 1938, the Germans added two new rotors, designated IV and V. The machine still had three slots for rotors, but the cipher clerk could now choose them from five. The number of possible arrangements increased from 6 to 60. For Polish methods, this meant a tenfold increase in requirements: instead of 6 sets of Zygalski's sheets, 60 were needed, which meant 1,560 sheets cut by hand, and instead of 6 bombs – 60. Producing 54 additional bombs exceeded the capabilities of the Cipher Bureau. To make matters worse, on January 1, 1939, the number of connections of the connector increased to 7–10, which significantly reduced the effectiveness of the bombs.

Even in this situation, the Poles achieved one more thing. The SS security service (SD) used the old procedure until July 1, 1939. Thanks to its messages, Rejewski reconstructed the wiring of both new rotors around the turn of 1938 and 1939. Poland thus knew the wiring of all five rotors, but no longer had the means to read all German communications daily.

The Kabacki Forest and the people of the Cipher Bureau

Until 1937, the German section worked in the Saski Palace in the center of Warsaw. In 1937, it was moved to a new complex of the General Staff in the Kabacki Forest near Pyr, south of the city. The complex on today's Kajakowa Street still exists and is used by the Air Force.

Behind the success of the mathematicians were people without whom their work would have had no chance. Gwido Langer, born on September 2, 1894, in Żyliń, raised in Cieszyn, had been directing the Radio Intelligence Section since January 15, 1929, and at least since mid-1931, the entire Cipher Bureau. He died in exile on March 30, 1948, in Kinross, Scotland, and in December 2010, his remains were brought back to Cieszyn. Maksymilian Ciężki, born on November 24, 1898, in Szamotuły, headed the German section BS-4 and was Langer's deputy. He led the daily work of the team. He died in London on November 9, 1951, spending the last three years of his life on welfare. Antoni Palluth, born on May 11, 1900, in Pobiedziska, a graduate of the Warsaw University of Technology, taught at a secret cryptology course in Poznań in 1929, where future Enigma breakers learned, and later, as one of the directors of AVA, was responsible for building their machines. He died on April 18, 1944, during an Allied bombing raid on the Sachsenhausen concentration camp.

Pyry, July 1939 – the secret handed over to the allies

In the spring of 1939, war was looming. In April, Germany abrogated the non-aggression pact with Poland. Poland was unable to keep up with the changes in the Enigma on its own, and Great Britain and France provided formal guarantees of assistance in the event of an attack. At an earlier meeting of cryptologists from the three countries in Paris in January 1939, all parties were still reserved, and no one revealed their cards. On June 30, 1939, the head of the Polish Cipher Bureau informed his French counterpart that "there is a new development in the situation." It was not about a new breakthrough, but rather a readiness to disclose the secret.

Who came to Kabacki Forest

Major Gustave Bertrand and Captain Henri Braquenié came from France. Great Britain was represented by Commander Alastair Denniston, head of the Government Code and Cypher School (later GCHQ), Alfred Dillwyn "Dilly" Knox, the main British specialist on the Enigma, and Commander Humphrey Sandwith from the Admiralty. The Polish side was represented by Langer, Ciężki, Colonel Stefan Mayer from the General Staff's Second Department, and three mathematicians: Rejewski, Różycki, and Zygalski.

For Bertrand, it was a surprise. Although he had brought the Schmidt documents to the Poles in 1932, it was only in Pyry, after six and a half years, that he learned that the Poles had long been reading the Enigma.

What the Poles conveyed

The Poles showed the guests everything: the theory, methods, and devices. It was decided that each delegation would receive a Polish replica of the Enigma made by AVA. The guests saw Zygalski's sheets and cryptologic bombs and learned the details of their construction. The British committed to producing two complete sets of sheets for all 60 rotor configurations in return – a task for which there were not enough hands in Warsaw. According to GCHQ, the British and French realized that the Poles were far ahead of them, both in terms of the amount of material read and the construction of the bomb, which GCHQ calls the first electromechanical device supporting cryptanalysis.

Knox's reaction

The most memorable scene of the meeting is Dilly Knox's reaction. The Brit had long been working on the Enigma and was stuck on the same problem as Rejewski: the connections between the keyboard and the input drum. His first question was reportedly: "What are the connections in the input drum?" When he heard that they ran simply alphabetically, he was astonished that the solution was so simple. British historian Gill Bennett writes on the blog of historians from the British Foreign Office that Knox was "furious that the solution turned out to be one he had dismissed himself," but he appreciated the Polish achievement, which, according to her, shortened the British attack on the Enigma by at least a year.

Knox also maintained a healthy skepticism. He noted that the Polish system was based on key repetition, which the Germans could "abolish at any moment" – and they indeed did so in the spring of 1940. Nevertheless, on August 1, 1939, he wrote to the Poles a letter thanking them for their "cooperation and patience," formulated in Polish. He included paper sticks and a scarf with a Derby horse racing motif – which is interpreted as a humorous acknowledgment that the Poles won this race.

The path of replicas to the West

In August 1939, two Polish replicas of the Enigma reached Paris, and Bertrand took one of them to London. The Intelligence Agency reports that the devices were sent to recipients by sea, which was considered the safest route at the time. Bertrand himself described in his memoirs that he handed it over at Victoria Station to Stewart Menzies from British intelligence SIS.

What resulted from this is certain. GCHQ writes that the knowledge gained in Poland "transformed the approach" of British cryptologists to the Enigma. In January 1940, Alan Turing traveled to just outside Paris to meet with Polish cryptologists who had been evacuated there, and his discussions with Rejewski were, according to GCHQ, fundamental to the concept of the first British bomb. The promised sets of sheets were produced by the British in John Jeffreys' section, and part of the second set reached the Poles in France on December 28, 1939. The ultimate impact of the read messages on the course of the war is a topic of historical debate – but without the meeting in Kabacki Forest, the British would have started their work from a much further point.

July 24, 25, or 26

It is surprising how difficult it is to establish the exact date of such an important meeting. Władysław Kozaczuk, the author of fundamental Polish works on the Enigma, stated July 25, 1939, and this date is accepted by many studies, while the Intelligence Agency writes about the visit in Pyry on July 25. GCHQ and the Intelligence Agency in Różycki's biography mention two days: July 25 and 26. The blog of historians from the British Foreign Office states July 26, while some studies mention July 26 and 27, and the English-language text from the Intelligence Agency states July 25–27. Some studies also mention a preliminary meeting in Warsaw on July 24. There is much to suggest that the discussions lasted longer than one day. The most frequently indicated date remains July 25, 1939, as the first day of the meeting.

War: Bruno, Cadix, and escape

September 1939: by train, truck, and through Kuty

When the war began on September 1, 1939, the secret of the Enigma was already in the hands of the British and French. Now it was necessary to save the people who knew it. On September 6, the Cipher Bureau left Warsaw by military train, the so-called echelon F, heading towards Mińsk Mazowiecki. On September 9, the cryptologists reached Brest, where the station was under German bombs. They continued by truck through Kowel and Łuck. Along the way, equipment related to the Enigma was destroyed to prevent it from falling into enemy hands.

On September 17, the day the Red Army entered, Rejewski, Zygalski, and Różycki crossed the Romanian border at Kuty. They avoided internment and reached Bucharest. They first knocked on the British embassy, which refused assistance. At the French embassy, it was enough to present a password: they introduced themselves as "friends of Bolek," referring to Captain Gustave Bertrand from French intelligence. They received passports under false names and visas, and a train took them to Paris. By the end of September 1939, they checked into the Viator hotel.

PC Bruno: a castle near Paris

From October 20, 1939, the Poles worked at a center codenamed PC Bruno. It was located in Château de Vignolles in Gretz-Armainvilliers, about 40 km southeast of Paris. It was headed by Bertrand, and the Polish group was led by Lieutenant Colonel Gwido Langer. It was a truly international team: about 15 Poles, 50 French, and seven Spanish republicans who dealt with Spanish and Italian ciphers.

Bruno operated in tandem with Bletchley Park from the start. In early December 1939, Langer and French Captain Henri Braquenié traveled to London and Bletchley. In the UK, John Jeffreys produced a complete set of Zygalski's sheets, prepared according to the Polish method, and in January 1940, Alan Turing himself brought them to France, spending a few days in Bruno discussing with his Polish colleagues. British GCHQ states today that Turing's discussions with Rejewski helped shape the design of the first British bomb.

The sheets worked quickly. On January 17, 1940, the Poles were the first to break the wartime Enigma: they read messages from October 28, 1939. By the fall of France in June 1940, Bruno had established 17 percent of all Enigma keys found by the Allies. In March 1940, both centers began reading some messages almost in real-time, and in the following months, several thousand messages were decrypted, roughly half on both sides of the English Channel.

The German offensive in the West interrupted this work. Just after midnight on June 10, 1940, Bertrand evacuated people from Gretz-Armainvilliers. After the fall of France on June 24, three planes transported the Poles and Spaniards to Algeria.

Cadix: cryptologists under Vichy watch

Africa was just a stop. In September 1940, the team returned to the unoccupied southern part of France, governed by the collaborationist Vichy regime. The new center was codenamed Cadix, after the Spanish Cádiz, and was located in Château des Fouzes near Uzès. There were 15 Poles, nine French, and seven Spaniards working there. Rejewski lived under the name Pierre Ranaud and was officially a teacher. Zygalski traveled from Algiers to Marseille on the passenger ship "Lamoricière" – the same one that sank a year and a half later with his colleague on board.

In Cadix, the focus was mainly on ciphers other than the Enigma. The center also had a branch in Algiers, which was headed by Major Maksymilian Ciężki from July 1941. It supported the Polish intelligence network known as the Africa Agency. People circulated between Uzès and Algiers, and each such journey across the Mediterranean was a risk.

The disaster of "Lamoricière"

On January 9, 1942, the ship "Lamoricière," sailing from Algiers to France, sank near the Balearics during a severe storm. Polish sources speak of mysterious circumstances surrounding the disaster. The number of victims varies depending on the source: Polish Wikipedia states 222 people, while studies about the ship mention close to 300. Among the victims was 32-year-old Jerzy Różycki, as well as Captain Jan Graliński, head of the Soviet section, cryptologist Piotr Smoleński, and the accompanying French Captain François Lane. In Warsaw, Różycki's son, Janusz, born in May 1939, was left behind. The father saw him for only a few months.

November 1942: the end of the free zone

On November 8, 1942, the Allies landed in North Africa. The Germans responded by occupying all of France. Bertrand evacuated Cadix on November 9, and German soldiers entered the estate three days later. The people dispersed, each looking for a way to Spain.

Rejewski and Zygalski left for Nice on November 11, and then frequently changed their locations to avoid drawing attention. On January 29, 1943, they set off across the Pyrenees. Just near the border, a guide terrorized them with a weapon and robbed them. They reached Spain, but were soon arrested. They were imprisoned in Seo de Urgel, and on March 24, they were transferred to Lleida (Lérida). Only with the help of the Polish Red Cross did they gain their freedom on May 4, 1943. From Madrid, they traveled to Portugal, and on the ship HMS "Scottish," they sailed to Gibraltar, from where on August 3, 1943, a Douglas DC-3 plane took them to Great Britain.

Boxmoor, not Bletchley

In Great Britain, the creators of the breakthrough regarding the Enigma did not end up at Bletchley Park. On August 16, 1943, Rejewski and Zygalski enlisted in the Polish Army as privates and were assigned to the Polish radio unit of the Supreme Commander in Stanmore-Boxmoor near London. They broke SS and SD codes, including a system called Doppelkassettenverfahren. Rejewski was promoted to second lieutenant, and on January 1, 1945, to lieutenant. His biography on the MacTutor website of St Andrews University directly states that the British missed the opportunity to utilize him at Bletchley. British cryptologist Alan Stripp noted that at Bletchley Park, due to secrecy rules, "little was known about the contributions of the Poles."

Langer, Ciężki, and Palluth: silence in captivity

Less fortunate were the commanders. On the night of March 10 to 11, 1943, Lieutenant Colonel Gwido Langer, Major Maksymilian Ciężki, Engineer Antoni Palluth, Edward Fokczyński, and Kazimierz Gaca tried to cross from France to Spain. A French guide betrayed them, and they fell into the hands of the Germans near Perpignan. Langer, according to PAP, spent the rest of the war in Stalag 122 in Compiègne and in the Eisenberg Castle in the Sudetes, repurposed into a camp.

What they did during interrogations was of immense importance. Langer mixed truth with lies: he admitted that before the war, the Poles had read the Enigma, but only sporadically, and during the war not at all. He then referred the interrogators to Ciężki, who convinced them that pre-war changes in the machine made further reading impossible. According to Colonel Stefan Mayer, no one from this group revealed the secret, allowing the Allies to benefit from the decryptions until the end of the war.

Antoni Palluth, co-founder of AVA, which built communication equipment and cryptographic devices for the military, did not live to see freedom. He ended up in the Sachsenhausen concentration camp and died there on April 18, 1944, during an Allied air raid. He was 43 years old.

Bletchley Park and Ultra

From the Polish file to the British factory

The meeting in Pyry near Warsaw in July 1939, according to GCHQ itself, changed the British approach to the Enigma. The British and French saw that the Poles were further ahead than they had expected, both in terms of the number of messages decrypted and the machine, which GCHQ calls the first electromechanical device supporting cryptanalysis. Bletchley Park took over this knowledge and built a large, almost industrial organization for breaking codes on it.

The scale is evident in the numbers. In January 1945, at its peak, 8,995 people worked at Bletchley and its facilities. About three-quarters of them were women, often with degrees in mathematics, physics, or engineering. At its best, about 4,000 messages were decrypted daily. Churchill called these people "the geese that laid golden eggs and never cackled."

The bomb and bombe: similar names, different machines

It is easy to confuse the Polish "cryptologic bomb" with the British bombe, but they are two different devices. The Polish bomb from 1938 exploited a weakness in the German procedure: the doubly sent key of the message in its header. It operated with three rotors and a small number of connections in the switchboard. When, at the turn of 1938 and 1939, the Germans added rotors and increased the number of connections, its usefulness dropped sharply.

Alan Turing designed a machine in 1939 based on a different idea: on "cribs," or fragments of text that were expected to be in the message, such as standard phrases in reports. The first bombe, named "Victory," was installed in Hut 1 on March 18, 1940. Gordon Welchman added the so-called diagonal board, which utilized the symmetry of the switchboard and significantly sped up the work. The second machine, "Agnus Dei," installed in August 1940, already had it. The construction was handled by engineer Harold Keen from the British Tabulating Machine Company. By the end of the war, about 200 British bombs had been created, primarily operated by Wrens, women from the Women's Royal Naval Service.

The huts with numbers

The work was divided among wooden huts, whose numbers became codenames. Hut 6, initially led by Welchman, broke the Enigma of the land forces and the Luftwaffe, while Hut 3 turned decrypted texts into intelligence reports. Hut 8 dealt with the Kriegsmarine Enigma. It was initially led by Turing, then by Hugh Alexander from November 1942, and by Patrick Mahon from September 1944. Hut 4 collaborated with Hut 8, translating and assessing the decrypted naval messages.

Naval Enigma and the Battle of the Atlantic

The codes of the German navy were the most difficult. The Kriegsmarine employed stricter procedures, and captured codebooks were needed to break them. Therefore, boarding actions proved to be so important. On May 9, 1941, the crew of the destroyer HMS "Bulldog" captured the U-boat U-110. The boarders, led by Lieutenant David Balme, took the Enigma machine and the short signal codebook. Operation "Primrose" was so secret that the ship was sunk, and Churchill only told Roosevelt about it in January 1942.

In February 1942, German submarines received a four-rotor Enigma, and Bletchley was blind for about ten months. The breakthrough came on the night of October 30, 1942, off the coast of Egypt. The damaged U-559 surfaced next to HMS "Petard," and the German crew abandoned the ship. Lieutenant Anthony Fasson, sailor Colin Grazier, and ship's canteen worker Tommy Brown boarded. They carried away codebooks, including the short signal book and the short weather cipher, but Fasson and Grazier drowned when the ship sank. Both were posthumously awarded the George Cross, and Brown received the George Medal. The materials obtained allowed for the reading of U-boat messages again, and in the later part of the war, the main work was done by American bombs built by NCR in Dayton, Ohio – 121 units, more efficient than the British ones.

Ultra: how valuable was it

In June 1941, British military intelligence assigned the codename Ultra to messages from decryptions. It encompassed not only the Enigma but also the teleprinter cipher Lorenza and Hagelin machines. How much Ultra changed the course of the war is still debated by historians, and it is worth presenting this as estimates rather than certainties. The official historian of British intelligence, Harry Hinsley, believed that without Ultra, the war would have lasted "two years longer, maybe three, maybe four." American intelligence researcher Jeffrey T. Richelson suggested that the shortening could have been just about three months, as that was how long it took to develop the American atomic bomb. Guy Hartcup wrote that it cannot be calculated in months or years. General Eisenhower wrote to the head of British intelligence, Stewart Menzies, in July 1945 that this information had "priceless value" for him.

The Germans believed in their machine

What is most astonishing is that the Germans did not fully believe until the end that the Enigma had been broken. Post-war interrogations revealed that their cryptologists considered the attack theoretically possible but requiring unrealistically large effort. Admiral Karl Dönitz suspected that his communications were being read, but he was never fully convinced of it. Meanwhile, by 1945, most of the German encrypted traffic using the Enigma was read by the Allies within a day or two. The maintenance of this illusion was also aided by the silence of Polish officers in German captivity.

What Happened Next

Marian Rejewski: Return to a Country That Preferred Not to Know

In November 1946, Rejewski was demobilized and returned to Poland, to his wife Irena and children in Bydgoszcz. His son Andrzej, born in 1936, died shortly after his father's return from a case of poliomyelitis. He was 11 years old. His daughter Janina was born in 1939.

The mathematician who outsmarted the German machine did not return to the university in Poznań. He worked in the sales department of the Kabel Polski factory in Bydgoszcz until he lost his job in 1950. Polish Wikipedia mentions unclear circumstances, while the MacTutor biography states that he was dismissed at the request of the security service. He then took on various jobs in cooperatives, and from 1954 he was an accountant in the provincial association of labor cooperatives. In February 1967, he retired.

Between 1949 and 1958, Rejewski was repeatedly checked by the UB and SB, suspected due to his service in the Polish Armed Forces in the West. The most interesting thing is what they did not find: according to MacTutor, the security service did not discover his role in breaking the Enigma throughout all those years. He remained silent until his retirement. Around that time, he wrote down his memories from his work in the Cipher Bureau, and the manuscript was sent to the Military Historical Institute.

In 1969, he moved to Warsaw. When the matter came to light in 1973, Rejewski suddenly became famous: newspapers wrote about him, and radio and television spoke of him. He published articles on the method of breaking the Enigma, corresponded with Bertrand, and at his request translated his book into Polish. On August 12, 1978, he received the Officer's Cross of the Order of Polonia Restituta. He died of a heart attack on February 13, 1980, in his Warsaw apartment, after returning from shopping. He was 74 years old. He was buried with military honors at the Military Cemetery in Powązki.

Henryk Zygalski: Mathematician from Liss

Zygalski did not return to Poland because he feared the communist authorities. The British did not recognize his Polish diploma, so he had to study again at Imperial College London to obtain teaching qualifications. In 1949, he received British citizenship. He taught mathematical statistics at the University of Surrey, an institution that evolved from the London Battersea College of Technology, which received university rights in 1966 and moved to Guildford between 1968 and 1970. Alan Turing's nephew, Dermot Turing, recalled that Zygalski was met with disdain due to his foreign qualifications.

In 1944, Zygalski met Bertha Blofield, a widow of a British officer, with whom he was associated for over 30 years. They lived in Liss in Hampshire. In 1977, the Polish University Abroad awarded him an honorary doctorate. Zygalski died on August 30, 1978. His ashes were scattered in the Garden of Remembrance at the crematorium in Chichester, where a plaque was unveiled in 2018. Bertha died a month after him.

The Różyccy: A Son Who Became an Olympian

Jerzy Różycki married Maria Barbara Majka in July 1938. Their son Janusz was born on May 10, 1939, in Warsaw, a few months before the outbreak of the war. He grew up to be a fencer and painter: he graduated from the Warsaw Academy of Fine Arts and won a silver Olympic medal in team foil at the Tokyo Games in 1964. The body of Jerzy Różycki was never found, and his only grave is a symbolic grave at the Bródno Cemetery in Warsaw.

Langer and Ciężki: A Cold Reception in London

Langer and Ciężki regained their freedom in 1945 and made their way through London to a Polish communications camp in Kinross, Scotland. They were received coldly, and Langer was blamed for his men being captured. He died on March 30, 1948, in Kinross and was buried in Perth at the Wellshill cemetery, alongside 381 Polish airmen. He lay there for 62 years. In December 2010, his remains were exhumed and reburied with honors in Cieszyn on December 10. Ciężki spent his last years on benefits. He died on November 9, 1951, in London, and in 2008, his remains were transferred to Szamotuły.

The Mystery Comes to Light and Memory

Thirty Years of Silence

In May 1945, Churchill asked everyone who had used Ultra never to reveal the source. For nearly three decades, silence prevailed in the United Kingdom, and full official recognition of the work of the people from Bletchley only came in July 2009. Poland was the first to break this silence. In 1967, Colonel Władysław Kozaczuk published the book "The Battle for Secrets," in which he was the first to reveal that Polish cryptologists had broken the Enigma before the war.

The real shock came in 1973 when Gustave Bertrand published the book "Enigma" in France. A year later, in 1974, Frederick Winterbotham published "The Ultra Secret." He wrote from memory, without access to archives, and his book was published in the year when the British ban on speaking about Ultra was lifted after 29 years. In Poland, the topic was picked up by cinema: in 1979, the film "The Secret of Enigma" directed by Roman Wionczek was made, and from November 14, 1980, television aired an eight-part series "The Enigma Mystery." Rejewski did not live to see the premiere of the series.

"U-571," or Hollywood Revises History

On April 21, 2000, the American film "U-571" was released in theaters. The plot shows how the crew of the US Navy captures an Enigma from a German submarine. In reality, the first naval Enigma from a U-boat was captured by the British from HMS "Bulldog" in May 1941, seven months before the USA entered the war. In the British Parliament, MP Brian Jenkins called the film an insult to the memory of British sailors, and Prime Minister Tony Blair agreed with him. President Bill Clinton, in a letter to MP Paul Truswell, acknowledged that it was just fiction. The credits included a dedication to the Allied sailors who captured Enigma materials, mentioning U-110, U-559, and the American capture U-505. Screenwriter David Ayer himself called this story a "distortion" in 2006.

Orders, Plaques, and Monuments

Recognition came gradually. In February 2000, President Aleksander Kwaśniewski posthumously awarded Rejewski, Różycki, and Zygalski the Grand Cross of the Order of Polonia Restituta. In 2002, a bilingual plaque was unveiled at Bletchley Park, naming them as the first to break the Enigma and stating that their work "greatly assisted" British cryptologists. In 2005, on the centenary of Rejewski's birth, a statue of him was erected in Bydgoszcz, and on November 10, 2007, a triangular monument to the three mathematicians, designed by Grażyna Bielska-Kozakiewicz and Mariusz Krzysztof Kozakiewicz, was unveiled in front of the Imperial Castle in Poznań, selected from 24 proposals.

In 2009, Poczta Polska issued a stamp featuring the three cryptologists. On August 5, 2014, the international engineering organization IEEE awarded them the title of IEEE Milestone for the first breaking of the Enigma from 1932 to 1939. On September 6, 2019, urns with soil from places associated with the cryptologists were placed in the crypt of the National Pantheon in Kraków. In November 2019, Ambassador Arkady Rzegocki unveiled a bronze plaque at the Polish church of St. Andrew Bobola in London, and in 2020, Jerzy Różycki was named the patron of the National Cybersecurity Center.

Enigma Cipher Center in Poznań

On September 24, 2021, the Enigma Cipher Center was officially opened in Poznań at 78 Święty Marcin Street, and from the next day, guests could visit it. The place has its own history. A building was erected here between 1843 and 1847 for the V Corps of the Prussian army, which housed the Poznań branch of the Cipher Bureau before the war, where the three mathematicians worked. The building, destroyed during the war, was not rebuilt, and in its place, the headquarters of the communist party was established, which was later used by historians from the University of Poznań until 2015. The center is a joint venture of the city and the university. The exhibition shows, among other things, how Zygalski's sheets, the cryptologic bomb, and the cyclometer worked.

New Anniversaries: 2025–2026

On July 1, 2025, the ORP "Jerzy Różycki," the first of two radio-electronic reconnaissance ships of the Dolphin program, built with the participation of Swedish Saab, was launched at the Remontowa Shipbuilding in Gdańsk. On January 14, 2026, the second ship, ORP "Henryk Zygalski," was launched. The ships, which are to gather information from radio waves, bear the names of the people who once extracted secrets from intercepted German radio messages. On August 16, 2025, on the 120th anniversary of Rejewski's birth, a Rejewski Picnic was held on Mill Island in Bydgoszcz, which was also attended by the Institute of National Remembrance, and in Łódź in 2025, roundabouts were named after the three mathematicians.

Interesting Facts About the Enigma

• It Started as a Business Machine. Arthur Scherbius filed a patent for a rotor cipher machine on February 23, 1918, and from 1923, the "commercial Enigma" was advertised. The German navy first introduced it in 1926, and the army by July 15, 1928.
• No Letter Could Encrypt Itself. This feature resulted from the action of the reversing drum and was one of the most valuable clues for cryptologists.
• The Number of Possible Settings for the military Enigma with three rotors and ten plugboard cables was 158,962,555,217,826,360,000.
• About 40,000 Copies of various versions of the Enigma were built.
• A Spy from a General's Family. Hans-Thilo Schmidt, codename Asché, who sold Enigma documents to the French, got a job in the German cipher office thanks to his brother, General Rudolf Schmidt. He was betrayed by his French handler Rodolphe Lemoine, who was captured by the Gestapo. Schmidt was arrested on April 1, 1943, and died in German custody in September 1943.
• The Swiss Enigma Also Fell. The Swiss used version K. It was broken by Poles, French, British, and Americans, who gave it the codename INDIGO.
• The Military Intelligence Abwehr Enigma had three rotors and a movable reversing drum but did not have a plugboard. Its codes were broken on December 8, 1941.
• After the War, Enigmas Were Sold. The Allies sold captured machines, still widely considered secure, to developing countries.
• Bletchley Became a Museum Only in the 90s. The Bletchley Park Trust was established in 1991, and the area was opened to visitors in 1993. The restored Hut 8 now houses an exhibition about HMS "Petard."
• Enigma from Underground. At the end of 2024, searchers from the Latebra Foundation excavated eight Enigma rotors and fragments of the casing on Sobieszewska Island in Gdańsk, alongside remnants of a radio station. Experts believe that the retreating Germans destroyed and buried the equipment at the end of the war to prevent it from falling into the hands of the Red Army.