Bomba ( cryptography ) The bomba , or bomba kryptologiczna ( Polish for " bomb " or " cryptologic bomb " ) was a special - purpose machine designed about October 1938 by Polish Cipher Bureau cryptologist Marian Rejewski to break German Enigma - machine cipher s . History . The German Enigma used a combination key to control the operation of the machine : rotor order , which rotors to install , which ring setting for each rotor , which initial setting for each rotor , and the settings of the " stecker " plugboard . The rotor settings were trigrams ( for example , " NJR " ) to indicate the way the operator was to set the machine . German Enigma operators were issued lists of these keys , one key for each day . For added security , however , each individual message was encrypted using an additional key modification . The operator randomly selected a trigram rotor setting for each message ( for example , " PDN " ) . This message key would be typed twice ( " PDNPDN " ) and encrypt ed , using the daily key ( all the rest of those settings ) . At this point each operator would reset his machine to the message key , which would then be used for the rest of the message . Because the configuration of the Enigma ' s rotor set changed with each depression of a key , the repetition would not be obvious in the ciphertext since the same plaintext letters would encrypt to different ciphertext letters . ( For example , " PDNPDN " might become " ZRSJVL . " ) This procedure , which seemed secure to the Germans , was nonetheless a cryptographic error . Using the knowledge that the first three letters of a message were the same as the second three , Polish mathematician – cryptologist Marian Rejewski was able to determine the internal wirings of the Enigma machine and thus to reconstruct the logical structure of the device . Only general traits of the machine were suspected , from the example of the commercial Enigma variant , which the Germans were known to have been using diplomatically . The military versions were sufficiently different that they presented an entirely new problem . Having done that much , it was still necessary to check each of the potential daily keys to break an encrypted message ( i . e . , a " ciphertext " ) . With many thousands of such possible keys , and with the growing complexity of the Enigma machine and its keying procedures , this was becoming an increasingly daunting task . In order to mechanize and speed up the process , Rejewski , a civilian mathematician working at the Polish General Staff ' s Cipher Bureau in Warsaw , invented the " " bomba kryptologiczna " " ( cryptologic bomb ) , probably in October 1938 . Each bomb ( six were built in Warsaw for the Cipher Bureau before September 1939 ) essentially constituted an electrically powered aggregate of six Enigmas and took the place of some one hundred workers . The bomb method was based , like the Poles ' earlier " grill " method , on the fact that the plug connections in the commutator ( " plugboard " ) did not change all the letters . But while the grill method required unchanged " pairs " of letters , the bomb method required only unchanged letters . Hence it could be applied even though the number of plug connections in this period was between five and eight . In mid - November 1938 the bombs were ready , and the reconstructing of daily keys now took about two hours . How the machine came to be called a " bomb " has been an object of fascination and speculation . One theory , most likely apocryphal , originated with Polish engineer and army officer Tadeusz Lisicki ( who knew Rejewski and his colleague Henryk Zygalski in wartime Britain but was never associated with the Cipher Bureau ) . He claimed that Jerzy Różycki ( the youngest of the three Enigma cryptologists , and who had died in a Mediterranean passenger - ship sinking in January 1942 ) named the " bomb " after an ice - cream dessert of that name . This story seems implausible . Rejewski himself stated that the device had been dubbed a " bomb " " for lack of a better idea . " Perhaps the most credible explanation is given by a Cipher Bureau technician , Czesław Betlewski : workers at B . S . - 4 , the Cipher Bureau ' s German section , christened the machine a " bomb " ( also , alternatively , a " washing machine " or a " mangle " ) because of the characteristic muffled noise that it produced when operating . According to a top - secret U . S . Army report dated 15 June 1945 , Up to July 25 , 1939 , the Poles had been breaking Enigma messages for over six and a half years without telling their French and British allies . On December 15 , 1938 , two new rotors , IV and V , were introduced ( three of the now five rotors being selected for use in the machine at a time ) . As Rejewski wrote in a 1979 critique of appendix 1 , volume 1 ( 1979 ) , of the official history of " British Intelligence in the Second World War " , " we quickly found the [ wirings ] within the [ new rotors ] , but [ their ] introduction [ . . . ] raised the number of possible sequences of drums from 6 to 60 [ . . . ] and hence also raised tenfold the work of finding the keys . Thus the change was not qualitative but quantitative . We would have had to markedly increase the personnel to operate the bombs , to produce the perforated sheets ( 60 series of 26 sheets each were now needed , whereas up to the meeting on July 25 , 1939 , we had only two such series ready ) and to manipulate the sheets . " Harry Hinsley suggested in " British Intelligence . . . " that the Poles decided to share their Enigma - breaking techniques and equipment with the French and British in July 1939 because they had encountered insuperable technical difficulties . Rejewski refuted this : " No , it was not [ cryptologic ] difficulties [ . . . ] that prompted us to work with the British and French , but only the deteriorating political situation . If we had had no difficulties at all we would still , or even the more so , have shared our achievements with our allies as our contribution to the struggle against Germany . "