Enigma machine An Enigma machine was any of a family of related electro - mechanical rotor cipher machines used in the twentieth century for enciphering and deciphering secret messages . Enigma was invented by the German engineer Arthur Scherbius at the end of World War I . Early models were used commercially from the early 1920s , and adopted by military and government services of several countries — most notably by Nazi Germany before and during World War II . Several different Enigma models were produced , but the German military models are the most commonly discussed . German military texts enciphered on the Enigma machine were first broken by the Polish Cipher Bureau , beginning in December 1932 . This success was a result of efforts by three Polish cryptologist s , Marian Rejewski , Jerzy Różycki and Henryk Zygalski , working for Polish military intelligence . Rejewski " reverse - engineered " the device , using theoretical mathematics and material supplied by French military intelligence . Subsequently the three mathematicians designed mechanical devices for breaking Enigma ciphers , including the cryptologic bomb . This work was an essential foundation to further work on decrypting ciphers from repeatedly modernized Enigma machines , first in Poland and after the outbreak of war in France and the UK . On 25 July 1939 , in Warsaw , the Poles initiated French and British military intelligence representatives into their Enigma - decryption techniques and equipment , including Zygalski sheets and the cryptologic bomb , and promised each delegation a Polish - reconstructed Enigma . Without these gifts of techniques and technology from Polish military intelligence , decryption of German Enigma messages during World War II at Bletchley Park would not have been possible , as it was based on using mathematical theory and the perfecting of methods , tools and devices — all invented and developed beginning in 1932 by Rejewski , Różycki and Zygalski . From 1938 onwards , additional complexity was repeatedly added to the Enigma machines , making decryption more difficult and necessitating larger numbers of equipment and personnel — more than the Poles could readily produce . The Polish breakthrough represented a vital basis for the later British continuation and effort . During the war , British cryptologist s decrypted a vast number of messages enciphered on Enigma . The intelligence gleaned from this source , codenamed " Ultra " by the British , was a substantial aid to the Allied war effort . Though Enigma had some cryptographic weaknesses , in practice it was German procedural flaws , operator mistakes , laziness , failure to systematically introduce changes in encipherment procedures , and Allied capture of key tables and hardware that , during the war , enabled Allied cryptologists to succeed . The exact influence of Ultra on the course of the war is debated ; an oft - repeated assessment is that decryption of German ciphers advanced the end of the European war by two years . Winston Churchill told the United Kingdom ' s King George VI after World War II : " It was thanks to Ultra that we won the war . " Design . Like other rotor machines , the Enigma machine is a combination of mechanical and electrical subsystems . The mechanical subsystem consists of a keyboard ; a set of rotating disks called " rotors " arranged adjacently along a spindle ; and one of various stepping components to turn one or more rotor with each key press . Electrical pathway . The mechanical parts act in such a way as to form a varying electrical circuit . When a key is pressed , a circuit is completed . Current flows through various components in their current configuration , ultimately lighting one display lamp , revealing an output letter . For example , when encrypting a message starting " ANX … " , the operator would first press the " A " key , and the " Z " lamp might light , so " Z " would be the first letter of the ciphertext . The operator would next press " N " , and then " X " in the same fashion , and so on . The detailed operation of Enigma is shown in the wiring diagram to the right . To simplify the example , only four components of a complete Enigma machine are shown . In reality , there are 26 lamps and keys , rotor wirings inside the rotors ( of which there are either three or four ) and between six and ten plug leads . Current flowed from the battery ( 1 ) through a depressed bi - directional keyboard switch ( 2 ) to the plugboard ( 3 ) . Next , it passed through the ( unused in this instance , so shown closed ) plug ( 3 ) via the entry wheel ( 4 ) , through the wiring of the three ( Wehrmacht Enigma ) or four ( " Kriegsmarine " M4 and " Abwehr " variants ) installed rotors ( 5 ) , and entered the reflector ( 6 ) . The reflector returned the current , via an entirely different path , back through the rotors ( 5 ) and entry wheel ( 4 ) , proceeding through plug ' S ' ( 7 ) connected with a cable ( 8 ) to plug ' D ' , and another bi - directional switch ( 9 ) to light the appropriate lamp . The repeated changes of electrical path through an Enigma scrambler implemented a polyalphabetic substitution cipher that provided Enigma ' s security . The diagram on the left shows how the electrical pathway changed with each key depression , which caused rotation of at least the right hand rotor . Current passed into the set of rotors , into and back out of the reflector , and out through the rotors again . The greyed - out lines are other possible paths within each rotor ; these are hard - wired from one side of each rotor to the other . The letter " A " encrypts differently with consecutive key presses , first to " G " , and then to " C " . This is because the right hand rotor has stepped , sending the signal on a completely different route . Eventually other rotors step with a key press . Rotors . The rotors ( alternatively " wheels " or " drums " , " Walzen " in German ) formed the heart of an Enigma machine . Each rotor was a disc approximately in diameter made from hard rubber or bakelite with brass spring - loaded pins on one face arranged in a circle ; on the other side are a corresponding number of circular electrical contacts . The pins and contacts represent the alphabet — typically the 26 letters A – Z ( this will be assumed for the rest of this description ) . When the rotors were mounted side - by - side on the spindle , the pins of one rotor rested against the contacts of the neighbouring rotor , forming an electrical connection . Inside the body of the rotor , 26 wires connected each pin on one side to a contact on the other in a complex pattern . Most of the rotors were identified by Roman numerals and each issued copy of rotor I was wired identically to all others . The same was true of the special thin beta and gamma rotors used in the M4 naval variant . By itself , a rotor performs only a very simple type of encryption — a simple substitution cipher . For example , the pin corresponding to the letter " E " might be wired to the contact for letter " T " on the opposite face , and so on . Enigma ' s security came from using several rotors in series ( usually three or four ) and the regular stepping movement of the rotors , thus implementing a poly - alphabetic substitution cipher . When placed in an Enigma , each rotor can be set to one of 26 possible positions . When inserted , it can be turned by hand using the grooved finger - wheel which protrudes from the internal Enigma cover when closed . So that the operator can know the rotor ' s position , each had an " alphabet tyre " ( or letter ring ) attached to the outside of the rotor disk , with 26 characters ( typically letters ) ; one of these could be seen through the window , thus indicating the rotational position of the rotor . In early models , the alphabet ring was fixed to the rotor disk . A later improvement was the ability to adjust the alphabet ring relative to the rotor disk . The position of the ring was known as the " Ringstellung " ( " ring setting " ) , and was a part of the initial setting prior to an operating session . In modern terms it was a part of the initialization vector . The rotors each contained a notch ( or more than one ) that controlled rotor stepping . In the military variants , the notches are located on the alphabet ring . The Army and Air Force Enigmas were used with several rotors ; initially three . On 15 December 1938 , this changed to five , from which three were chosen for a given session . Rotors were marked with Roman numerals to distinguish them : I , II , III , IV and V , all with single notches located at different points on the alphabet ring . This variation was probably intended as a security measure , but ultimately allowed the Polish Clock Method and British Banburismus attacks . The Naval version of the " Wehrmacht " Enigma had always been issued with more rotors than the other services : at first six , then seven , and finally eight . The additional rotors were marked VI , VII and VIII , all with different wiring , and had two notches , resulting in more frequent turnover . The four - rotor Naval Enigma ( M4 ) machine accommodated an extra rotor in the same space as the three - rotor version . This was accomplished by replacing the original reflector with a thinner one and by adding a thin fourth rotor . That fourth rotor was one of two types , " Beta " or " Gamma " , and never stepped , but could be manually set to any of 26 positions . One of the 26 made the machine perform identically to the three - rotor machine . Stepping . To avoid merely implementing a simple ( and easily breakable ) substitution cipher , every key press caused one or more rotors to step by one twenty - sixth of a full rotation , before the electrical connections were made . This changed the substitution alphabet used for encryption , ensuring that the cryptographic substitution was different at each new rotor position , producing a more formidable polyalphabetic substitution cipher . The stepping mechanism varied slightly from model to model . The right - hand rotor stepped once with each keystroke , and other rotors stepped less frequently . Turnover . The advancement of a rotor other than the left - hand one was called a " turnover " by the British . This was achieved by a ratchet and pawl mechanism . Each rotor had a ratchet with 26 teeth and every time a key was pressed , the set of spring - loaded pawls moved forward in unison , trying to engage with a ratchet . The alphabet ring of the rotor to the right normally prevented this . As this ring rotated with its rotor , a notch machined into it would eventually align itself with the pawl , allowing it to engage with the ratchet , and advance the rotor on its left . The right - hand pawl , having no rotor and ring to its right , stepped its rotor with every key depression . For a single - notch rotor in the right - hand position , the middle rotor stepped once for every 26 steps of the right - hand rotor . Similarly for rotors two and three . For a two - notch rotor , the rotor to its left would turn over twice for each rotation . The first five rotors to be introduced ( I – V ) contained one notch each , while the additional naval rotors VI , VII and VIII each had two notches . The position of the notch on each rotor was determined by the letter ring which could be adjusted in relation to the core containing the interconnections . The points on the rings at which they caused the next wheel to move were as follows . The design also included a feature known as " double - stepping " . This occurred when each pawl aligned with both the ratchet of its rotor and the rotating notched ring of the neighbouring rotor . If a pawl engaged with a ratchet through alignment with a notch , as it moved forward it pushed against both the ratchet and the notch , advancing both rotors . In a three - rotor machine , double - stepping affected rotor two only . If in moving forward the ratchet of rotor three was engaged , rotor two would move again on the subsequent keystroke , resulting in two consecutive steps . Rotor two also pushes rotor one forward after 26 steps , but since rotor one moves forward with every keystroke anyway , there is no double - stepping . This double - stepping caused the rotors to deviate from odometer - style regular motion . With three wheels and only single notches in the first and second wheels , the machine had a period of 26 × 25 × 26 = 16 , 900 ( not 26 × 26 × 26 , because of double - stepping ) . Historically , messages were limited to a few hundred letters , and so there was no chance of repeating any combined rotor position during a single session , denying cryptanalysts valuable clues . To make room for the Naval fourth rotors , the reflector was made much thinner . The fourth rotor fit into the space made available . No other changes were made , which eased the changeover . Since there were only three pawls , the fourth rotor never stepped , but could be manually set into one of 26 possible positions . A device that was designed , but not implemented before the war ' s end , was the " Lückenfüllerwalze " ( gap - fill wheel ) that implemented irregular stepping . It allowed field configuration of notches in all 26 positions . If the number of notches was a relative prime of 26 and the number of notches were different for each wheel , the stepping would be more unpredictable . Like the Umkehrwalze - D it also allowed the internal wiring to be reconfigured . Entry wheel . The current entry wheel ( " Eintrittswalze " in German ) , or entry stator , connects the plugboard to the rotor assembly . If the plugboard is not present , the entry wheel instead connects the keyboard and lampboard to the rotor assembly . While the exact wiring used is of comparatively little importance to security , it proved an obstacle to Rejewski ' s progress during his study of the rotor wirings . The commercial Enigma connects the keys in the order of their sequence on the keyboard : " Q " formula _ 1 " A " , " W " formula _ 1 " B " , " E " formula _ 1 " C " and so on . However , the military Enigma connects them in straight alphabetical order : " A " formula _ 1 " A " , " B " formula _ 1 " B " , " C " formula _ 1 " C " , and so on . It took inspired guesswork for Rejewski to penetrate the modification . Reflector . With the exception of models A and B , the last rotor came before a " reflector " ( German : " Umkehrwalze " , meaning " reversal rotor " ) , a patented feature unique to Enigma among the period ' s various rotor machines . The reflector connected outputs of the last rotor in pairs , redirecting current back through the rotors by a different route . The reflector ensured that Enigma is self - reciprocal : conveniently , encryption was the same as decryption . However , the reflector also gave Enigma the property that no letter ever encrypted to itself . This was a severe conceptual flaw and a cryptological mistake subsequently exploited by codebreakers . In Model C , the reflector could be inserted in one of two different positions . In Model D , the reflector could be set in 26 possible positions , although it did not move during encryption . In the " Abwehr " Enigma , the reflector stepped during encryption in a manner like the other wheels . In the German Army and Air Force Enigma , the reflector was fixed and did not rotate ; there were four versions . The original version was marked A , and was replaced by Umkehrwalze " B on 1 November 1937 . A third version , Umkehrwalze " C was used briefly in 1940 , possibly by mistake , and was solved by Hut 6 . The fourth version , first observed on 2 January 1944 , had a rewireable reflector , called " Umkehrwalze " D , allowing the Enigma operator to alter the connections as part of the key settings . Plugboard . The plugboard ( " Steckerbrett " in German ) permitted variable wiring that could be reconfigured by the operator ( visible on the front panel of Figure 1 ; some of the patch cords can be seen in the lid ) . It was introduced on German Army versions in 1930 , and was soon adopted by the Navy . The plugboard contributed more cryptographic strength than an extra rotor . Enigma without a plugboard ( known as " unsteckered Enigma " ) can be solved relatively straightforwardly using hand methods ; these techniques are generally defeated by the plugboard , driving Allied cryptanalysts to special machines to solve it . A cable placed onto the plugboard connected letters in pairs ; for example , " E " and " Q " might be a steckered pair . The effect was to swap those letters before and after the main rotor scrambling unit . For example , when an operator presses " E " , the signal was diverted to " Q " before entering the rotors . Up to 13 steckered pairs might be used at one time , although only 10 were normally used . Current flowed from the keyboard through the plugboard , and proceeded to the entry - rotor or " Eintrittswalze " . Each letter on the plugboard had two jacks . Inserting a plug disconnected the upper jack ( from the keyboard ) and the lower jack ( to the entry - rotor ) of that letter . The plug at the other end of the crosswired cable was inserted into another letter ' s jacks , thus switching the connections of the two letters . Accessories . Other features made various Enigma machines more secure or more convenient . Some M4 Enigmas used the " Schreibmax " , a small printer that could print the 26 letters on a narrow paper ribbon . This eliminated the need for a second operator to read the lamps and transcribe the letters . The " Schreibmax " was placed on top of the Enigma machine and was connected to the lamp panel . To install the printer , the lamp cover and light bulbs had to be removed . It improved both convenience and operational security ; the printer could be installed remotely such that the signal officer operating the machine no longer had to see the decrypted plaintext . Another accessory was the remote lamp panel " Fernlesegerät " . For machines equipped with the extra panel , the wooden case of the Enigma was wider and could store the extra panel . A lamp panel version could be connected afterwards , but that required , as with the " Schreibmax " , that the lamp panel and lightbulbs be removed . The remote panel made it possible for a person to read the decrypted plaintext without the operator seeing it . In 1944 , the " Luftwaffe " introduced a plugboard switch , called the " Uhr " ( clock ) , a small box containing a switch with 40 positions . It replaced the standard plugs . After connecting the plugs , as determined in the daily key sheet , the operator turned the switch into one of the 40 positions , each producing a different combination of plug wiring . Most of these plug connections were , unlike the default plugs , not pair - wise . In one switch position , the " Uhr " did not swap letters , but simply emulated the 13 stecker wires with plugs . Mathematical analysis . The Enigma transformation for each letter can be specified mathematically as a product of permutation s . Assuming a three - rotor German Army / Air Force Enigma , let formula _ 7 denote the plugboard transformation , formula _ 8 denote that of the reflector , and formula _ 9 denote those of the left , middle and right rotors respectively . Then the encryption formula _ 10 can be expressed as After each key press , the rotors turn , changing the transformation . For example , if the right hand rotor formula _ 12 is rotated formula _ 13 positions , the transformation becomes formula _ 14 , where formula _ 15 is the cyclic permutation mapping " A " to " B " , " B " to " C " , and so forth . Similarly , the middle and left - hand rotors can be represented as formula _ 16 and formula _ 17 rotations of formula _ 18 and formula _ 19 . The encryption transformation can then be described as Combining three rotors from a set of five , the rotor settings with 26 positions , and the plugboard with ten pairs of letters connected , the military Enigma has 158 , 962 , 555 , 217 , 826 , 360 , 000 ( 158 quintillion ) different settings . Operation . In use , the Enigma required a list of daily key settings and auxiliary documents . The procedures for German Naval Enigma were more elaborate and more secure than those in other services . Navy codebook s were printed in red , water - soluble ink on pink paper so that they could easily be destroyed if they were endangered . The codebook to the right was taken from captured . In German military practice , communications were divided up into separate networks , each using different settings . These communication nets were termed " keys " at Bletchley Park , and were assigned code name s , such as " Red " , " Chaffinch " , and " Shark " . Each unit operating in a network was assigned a settings list for its Enigma for a period of time . For a message to be correctly encrypted and decrypted , both sender and receiver had to configure their Enigma in the same way ; rotor selection and order , starting position and plugboard connections must be identical . All these settings ( together the key in modern terms ) were established beforehand , distributed in codebook s . An Enigma machine ' s initial state , the cryptographic key , has several aspects : Note that although the " ringstellung " was a required part of the setup , they did not affect encryption because the rotors were positioned independently of the rings . The ring settings were only necessary to determine the initial rotor position based on the " message setting " that was transmitted at the beginning of a message , as described in the " Indicators " section , below . Once the receiver ' s rotors were set to the indicated positions , the ring settings no longer played any role . In modern cryptographic language , the ring settings did not actually contribute entropy to the key used for encrypting the message . Rather , the ring settings were part of a separate key ( along with the rest of the setup such as wheel order and plug settings ) used to encrypt an " initialization vector " for the message . The session key consisted of the complete setup " except for " the ring settings , plus the initial rotor positions chosen arbitrarily by the sender ( the " message setting " ) . The important part of this session key was the rotor positions , not the ring positions . However , by " encoding " the rotor position into the ring position using the ring settings , additional variability was added to the encryption of the initialization vector . Enigma was designed to be secure even if the rotor wiring was known to an opponent , although in practice considerable effort protected the wiring configuration . If the wiring is secret , the total number of possible configurations has been calculated to be around 10 ( approximately 380 bits ) ; with known wiring and other operational constraints , this is reduced to around 10 ( 76 bits ) . Users of Enigma were confident of its security because of the large number of possibilities ; it was not then feasible for an adversary to even begin to try a brute force attack . Indicator . Most of the key was kept constant for a set time period , typically a day . However , a different initial rotor position was used for each message , a concept similar to an initialisation vector in modern cryptography . The reason is that encrypting many messages with identical or near - identical settings ( termed in cryptanalysis as being " in depth " ) , would enable an attack using a statistical procedure such as Friedman ' s Index of coincidence . The starting position for the rotors was transmitted just before the ciphertext , usually after having been enciphered . The exact method used was termed the " indicator procedure " . Design weakness and operator sloppiness in these indicator procedures were two of the main weakness that made cracking Enigma possible . One of the earliest " indicator procedures " was used by Polish cryptanalysts to make the initial breaks into the Enigma . The procedure was for the operator to set up his machine in accordance with his settings list , which included a global initial position for the rotors ( " Grundstellung " , meaning " ground setting " ) , say , " AOH " . The operator turned his rotors until " AOH " was visible through the rotor windows . At that point , the operator chose his own arbitrary starting position for that particular message . An operator might select " EIN " , and these became the " message settings " for that encryption session . The operator then typed " EIN " into the machine , twice , to allow for detection of transmission errors . The results were an encrypted indicator — the " EIN " typed twice might turn into " XHTLOA " , which would be transmitted along with the message . Finally , the operator then spun the rotors to his message settings , " EIN " in this example , and typed the plaintext of the message . At the receiving end , the operation was reversed . The operator set the machine to the initial settings and typed in the first six letters of the message ( " XHTLOA " ) . In this example , " EINEIN " emerged on the lamps . After moving his rotors to " EIN " , the receiving operator then typed in the rest of the ciphertext , deciphering the message . The weakness in this indicator scheme came from two factors . First , use of a global ground setting — this was later changed so the operator selected his initial position to encrypt the indicator , and sent the initial position in the clear . The second problem was the repetition of the indicator , which was a serious security flaw . The message setting was encoded twice , resulting in a relation between first and fourth , second and fifth , and third and sixth character . This security problem enabled the Polish Cipher Bureau to break into the pre - war Enigma system as early as 1932 . However , from 1940 on , the Germans changed procedure . During World War II , codebooks were only used each day to set up the rotors , their ring settings and the plugboard . For each message , the operator selected a random start position , let ' s say " WZA " , and a random message key , perhaps " SXT " . He moved the rotors to the " WZA " start position and encoded the message key " SXT " . Assume the result was " UHL " . He then set up the message key , " SXT " , as the start position and encrypted the message . Next , he transmitted the start position , " WZA " , the encoded message key , " UHL " , and then the ciphertext . The receiver set up the start position according to the first trigram , " WZA " , and decoded the second trigram , " UHL " , to obtain the " SXT " message setting . Next , he used this " SXT " message setting as the start position to decrypt the message . This way , each ground setting was different and the new procedure avoided the security flaw of double encoded message settings . This procedure was used by " Wehrmacht " and " Luftwaffe " only . The " Kriegsmarine " procedures on sending messages with the Enigma were far more complex and elaborate . Prior to encryption the message was encoded using the " Kurzsignalheft " code book . The " Kurzsignalheft " contained tables to convert sentences into four - letter groups . A great many choices were included , for example , logistic matters such as refueling and rendezvous with supply ships , positions and grid lists , harbor names , countries , weapons , weather conditions , enemy positions and ships , date and time tables . Another codebook contained the " Kenngruppen " and " Spruchschlüssel " : the key identification and message key . Additional details . The Army Enigma machine used only the 26 alphabet characters . Signs were replaced with rare character combinations . A space was omitted or replaced with an X . The X was generally used as point or full - stop . Some signs were different in other parts of the armed forces . The " Wehrmacht " replaced a comma with ZZ and the question sign with FRAGE or FRAQ . The " Kriegsmarine " replaced the comma with Y and the question sign with UD . The combination CH , as in " Acht " ( eight ) or " Richtung " ( direction ) , was replaced with Q ( AQT , RIQTUNG ) . Two , three and four zeros were replaced with CENTA , MILLE and MYRIA . The " Wehrmacht " and the " Luftwaffe " transmitted messages in groups of five characters . The " Kriegsmarine " , using the four rotor Enigma , had four - character groups . Frequently used names or words were varied as much as possible . Words like " Minensuchboot " ( minesweeper ) could be written as MINENSUCHBOOT , MINBOOT , MMMBOOT or MMM354 . To make cryptanalysis harder , messages were limited to 250 characters . Longer messages were divided into several parts , each using a different message key . History . The Enigma family included multiple designs . The earliest were commercial models dating from the early 1920s . Starting in the mid - 1920s , the German military began to use Enigma , making a number of security - related changes . Various nations either adopted or adapted the design for their own cipher machines . Commercial Enigma . On 23 February 1918 , German engineer Arthur Scherbius applied for a patent for a cipher machine using rotors and , with E . Richard Ritter , founded the firm of Scherbius & Ritter . They approached the German Navy and Foreign Office with their design , but neither was interested . They then assigned the patent rights to Gewerkschaft Securitas , who founded the " Chiffriermaschinen Aktien - Gesellschaft " ( Cipher Machines Stock Corporation ) on 9 July 1923 ; Scherbius and Ritter were on the board of directors . Chiffriermaschinen AG began advertising a rotor machine — " Enigma model A " — which was exhibited at the Congress of the International Postal Union in 1923 - 1924 . The machine was heavy and bulky , incorporating a typewriter . It measured 65×45×35 cm and weighed about . In 1925 Enigma " model B " was introduced , and was of a similar construction . While bearing the Enigma name , both models " A " and " B " were quite unlike later versions : they differed in physical size and shape , but also cryptographically , in that they lacked the reflector . The reflector — suggested by Scherbius ' s colleague Willi Korn — was introduced in " Enigma C " ( 1926 ) . " Model C " was smaller and more portable than its predecessors . It lacked a typewriter , relying on the operator ; hence the informal name of " glowlamp Enigma " to distinguish it from models " A " and " B " . The " Enigma C " quickly gave way to " Enigma D " ( 1927 ) . This version was widely used , with shipments to Sweden , the Netherlands , United Kingdom , Japan , Italy , Spain , United States and Poland . Enigma D was intercepted by the Poles on a Friday in late December 1927 at the Polish railroad customs house in Warsaw . A heavy package had arrived there , addressed to the German Embassy . A German representative of the " radio " company that had shipped the package , repeatedly called customs officials , stating that the package had been shipped by mistake , must not go through customs inspection , and must be returned to Berlin immediately . His calls became increasingly frantic , until custom officials became suspicious and notified the Polish Cipher Bureau , which was then responsible for radio - related matters . Polish intelligence Stefan Mayer had his agents secretly move the package to a secure location . The package contained a cipher machine visually identical with commercial Enigma machines . The agents correctly guessed that the Germans had modified the wiring ; they carefully noted the changes . The machine was reassembled and returned to the radio company in Berlin . When Major Gwido Langer took over the newly organized Cipher Bureau in 1929 , he possessed the modified Enigma machine , but he did not reveal this to the newly recruited mathematics students , Marian Rejewski , Henryk Zygalski and Jerzy Róźycki . Langer correctly assumed that the Germans would make further modifications to the Enigma machine , and he provided Rejewski only with a commercial machine , wanting his cryptologists to understand the machine from a purely mathematical point of view . Military Enigma . The Navy was the first military branch to adopt Enigma . This version , named " Funkschlüssel C " ( " Radio cipher C " ) , had been put into production by 1925 and was introduced into service in 1926 . The keyboard and lampboard contained 29 letters — A - Z , Ä , Ö and Ü — which were arranged alphabetically , as opposed to the QWERTZU ordering . The rotors had 28 contacts , with the letter " X " wired to bypass the rotors unencrypted . Three rotors were chosen from a set of five and the reflector could be inserted in one of four different positions , denoted α , β , γ and δ . The machine was revised slightly in July 1933 . By 15 July 1928 , the German Army ( " Reichswehr " ) had introduced their own version of the Enigma — the " Enigma G " , revised to the " Enigma I " by June 1930 . Enigma I is also known as the " Wehrmacht " , or " Services " Enigma , and was used extensively by German military services and other government organisations ( such as the railways ) , before and during World War II . The major difference between " Enigma I " and commercial Enigma models was the addition of a plugboard to swap pairs of letters , greatly increasing cryptographic strength . Other differences included the use of a fixed reflector and the relocation of the stepping notches from the rotor body to the movable letter rings . The machine measured 28×34×15 cm ( 11 in×13 . 5 in×6 in ) and weighed around . By 1930 , the Army had suggested that the Navy adopt their machine , citing the benefits of increased security ( with the plugboard ) and easier interservice communications . The Navy eventually agreed and in 1934 brought into service the Navy version of the Army Enigma , designated " Funkschlüssel " ' or " M3 " . While the Army used only three rotors at that time , the Navy specified a choice of three from a possible five . In December 1938 , the Army issued two extra rotors so that the three rotors were chosen from a set of five . In 1938 , the Navy added two more rotors , and then another in 1939 to allow a choice of three rotors from a set of eight . In August 1935 , the Air Force introduced the Wehrmacht Enigma for their communications . A four - rotor Enigma was introduced by the Navy for U - boat traffic on 1 February 1942 , called " M4 " ( the network was known as " Triton " , or " Shark " to the Allies ) . The extra rotor was fitted in the same space by splitting the reflector into a combination of a thin reflector and a thin fourth rotor . There was also a large , eight - rotor printing model , the " Enigma II " . In 1933 the Polish Cipher Bureau detected that it was in use for high - level military communications , but that it was soon withdrawn , as it was unreliable and jammed frequently . The " Abwehr " used the " Enigma G " ( the " Abwehr " Enigma ) . This Enigma variant was a four - wheel unsteckered machine with multiple notches on the rotors . This model was equipped with a counter which incremented upon each key press , and so is also known as the " counter machine " or the " Zählwerk " Enigma . During World War II the Abwehr used these machines to control and report the locations of submarines in the Atlantic and to pass information about bombing raids , the movement of military units , and the location and cargo of military supply ships . Before Enigma Britain was in danger of being starved into submission and after it the roles were virtually reversed . The British moved one step ahead of the Germans and began sinking submarines faster than they could be built . Other militaries . Other countries used Enigma machines . The Italian Navy adopted the commercial Enigma as " Navy Cipher D " . The Spanish also used commercial Enigma during their Civil War . British codebreakers succeeded in breaking these machines , which lacked a plugboard . The Swiss used a version of Enigma called " model K " or " Swiss K " for military and diplomatic use , which was very similar to commercial Enigma D . The machine was cracked by Poland , France , the United Kingdom and the United States ( the latter codenamed it INDIGO ) . An " Enigma T " model ( codenamed " Tirpitz " ) was used by Japan . An estimated 100 , 000 Enigma machines were constructed . After the end of World War II , the Allies sold captured Enigma machines , still widely considered secure , to a number of developing countries . Surviving machines . The effort to break the Enigma was not disclosed until the 1970s . Since then , interest in the Enigma machine has grown . Enigmas are on public display in museums around the world . The Deutsches Museum in Munich has both the three - and four - rotor German military variants , as well as several civilian versions . Enigma machines are exhibited at the National Codes Centre in Bletchley Park , the Government Communications Headquarters , the Science Museum in London , the Polish Institute and Sikorski Museum in London , the Polish Army Museum in Warsaw , the " Armémuseum " ( Swedish Army Museum ) in Stockholm , the National Signals Museum in Finland , and at the Australian War Memorial and in the foyer of the Defence Signals Directorate , both in Canberra , Australia . In the United States , Enigma machines can be seen at the Computer History Museum in Mountain View , California , and at the National Security Agency ' s National Cryptologic Museum in Fort Meade , Maryland , where visitors can try their hand at enciphering and deciphering messages . Two machines that were acquired after the capture of during World War II are on display at the Museum of Science and Industry in Chicago , Illinois . The San Diego State University Library has a machine . In Canada , a Swiss Army issue Enigma - K , is in Calgary , Alberta . It is on permanent display at the Naval Museum of Alberta inside the Military Museums of Calgary . A 3 - rotor Enigma machine is on display at the Communications and Electronics Engineering ( CELE ) Museum in Kingston , Ontario , at Canadian Forces Base ( CFB ) Kingston . Occasionally , Enigma machines are sold at auction ; prices have in recent years ranged from US $ 40 , 000 to US $ 203 , 000 in 2011 . Replicas are available in various forms , including an exact reconstructed copy of the Naval M4 model , an Enigma implemented in electronics ( Enigma - E ) , various simulators and paper - and - scissors analogues . A rare " Abwehr " Enigma machine , designated G312 , was stolen from the Bletchley Park museum on 1 April 2000 . In September , a man identifying himself as " The Master " sent a note demanding £25 , 000 and threatening to destroy the machine if the ransom were not paid . In early October 2000 , Bletchley Park officials announced that they would pay the ransom , but the stated deadline passed with no word from the blackmailer . Shortly afterward , the machine was sent anonymously to BBC journalist Jeremy Paxman , missing three rotors . In November 2000 , an antiques dealer named Dennis Yates was arrested after telephoning " The Sunday Times " to arrange the return of the missing parts . The Enigma machine was returned to Bletchley Park after the incident . In October 2001 , Yates was sentenced to 10 months in prison and served three months . In October 2008 , the Spanish daily newspaper " El País " reported that 28 Enigma machines had been discovered by chance in an attic of Army headquarters in Madrid . These 4 - rotor commercial machines had helped Franco ' s Nationalists win the Spanish Civil War because , though the British cryptologist Alfred Dilwyn Knox in 1937 broke the cipher generated by Franco ' s Enigma machines , this was not disclosed to the Republicans , who failed to break the cipher . The Nationalist government continued using its 50 Enigmas into the 1950s . Some machines have gone on display in Spanish military museums , including one at the National Museum of Science and Technology ( MUNCYT ) in A Coruña . Two have been given to Britain ' s GCHQ . The Bulgarian military used Enigma machines with a Cyrillic keyboard ; one is on display in the National Museum of Military History in Sofia . Derivatives . The Enigma was influential in the field of cipher machine design , spinning off other rotor machines . The British Typex was originally derived from the Enigma patents ; Typex even includes features from the patent descriptions that were omitted from the actual Enigma machine . The British paid no royalties for the use of the patents , to protect secrecy . The Typex implementation is not the same as that found in German or other Axis versions . A Japanese Enigma clone was codenamed GREEN by American cryptographers . Little used , it contained four rotors mounted vertically . In the U . S . , cryptologist William Friedman designed the M - 325 , a machine logically similar , although not in construction . A unique rotor machine was constructed in 2002 by Netherlands - based Tatjana van Vark . This device makes use of 40 - point rotors , allowing letters , numbers and some punctuation to be used ; each rotor contains 509 parts . Machines like the SIGABA , NEMA , Typex and so forth , are deliberately not considered to be Enigma derivatives as their internal ciphering functions are not mathematically identical to the Enigma transform . Several software implementations exist , but not all exactly match Enigma behavior . The most commonly used software derivative ( that is not compliant with any hardware implementation of the Enigma ) is at EnigmaCo . de . Many Java applet Enigmas only accept single letter entry , complicating use even if the applet is Enigma compliant . Technically , Enigma @ home is the largest scale deployment of a software Enigma , but the decoding software does not implement encipherment making it a derivative ( as all original machines could cipher and decipher ) . A user - friendly 3 - rotor simulator , where users can select rotors , use the plugboard and define new settings for the rotors and reflectors is available . The output appears in separate windows which can be independently made " invisible " to hide decryption . Another includes an " autotyping " function which takes plaintext from a clipboard and converts it to cyphertext ( or vice - versa ) at one of four speeds . The " very fast " option produces 26 characters in less than one second .