The assumption that the Polish mathematicians working for the military intelligence broke the code once and then only due to some additional action taken by Germans it was necessary to break the code once more, although correct to some extent is not really that accurate, as the decryption of the Enigma codes was a continuous process rather than few events separated by a relatively long time. This was caused by a simple fact that Germans were developing the device for decades, steadily increasing complexity and sophistication of the new version.

Enigma device has been built by Artur Scherbius and Hugo Koch in 1918 and entered initial phase of production in the same year, although it entered a relatively wider use only in the early 1920, both in Germany and then also other countries. Enigma entered usage in German navy in 1926 and two years later it also has been adopted by German land forces.The code used by Enigma devices or, to be more precise, the mechanism of operation of the machine has been reverse-engineered by the Polish mathematicians, Marian Rejewski, Jerzy Różycki and Henryk Zygalski in 1932. The Bureau of Ciphers, a signal intelligence unit within the Polish Army HQ managed to buy a civilian version of Enigma. In addition, Polish intelligence was informed by customs officers working at the Warsaw airport that an employee of a German embassy aggressively demanded immediate return of a certain misplaced package and managed to check its contents and after learning it was another cypher machine, they photographed it thoroughly before returning the device. Thus, Polish cryptographers had the civilian version of device and possessed limited but still important knowledge of the newer version, allowing them to extrapolate the direction of device development.

Polish cryptographers finally managed to break the code in 1932, although their methods were based on the three-rotor version of Enigma device that has been used by Germans. Using mathematical models, information received from French intelligence, analysis of the actual device and, last but not least, errors and mistakes of the Enigma operators, they were able to decipher most of the encrypted communications. But Germans were still developing the machine while security specialists were analyzing the everyday usage of the device, addressing found issues. Nevertheless, in the period between the end of 1932 and early 1937, Polish military intelligence was able to decipher messages encrypted by Enigma with relative ease.

This changed in 1937, when Germans intensified the development of Enigma and introduced new procedures, such as increased frequency of rotor re-configuration (since 1st October 1937 it was changed daily) and resigned from dividing the messages into several parts with each subsequent part starting with the same word FORT (abbreviation of German Fortsetzung, i.e. 'continuation'). Procedures of the code transmission were also changed. Rejewski managed to address these issues by using the fact that with three rotors, they could have been only set in six different configuration and building a device nicknamed 'The Bomb' that was composed of six linked Enigma machines allowing for faster decryption of the daily codes (the 'Bomb' was used only to establish the encryption key hidden in the header of the message, never the message itself).

In the late 1938 Germans introduced two additional rotors and although the machines still were able to use only three rotors at the time, the ability to select three out of five possible encryption settings significantly increased difficulty of decryption. This change increased the number of the possible rotor combinations to 60, and although the internal construction of the two new rotors was quickly deduced and it was technically possible to simply expand 'The Bomb' by linking 60 copies of Enigma machine, the cost of such enterprise was beyond the budget capability of the Bureau of Ciphers. In addition, increased number of plugboard links (causing the selected letters in the encrypted text to be switched by one another) furthermore increased the complexity of encryption. Last but not least, Germans eventually phased out the double-encryption of the header containing the cipher settings that made the encryption easier, as Poles knew about the double-encryption (by the same code) what helped in decryption by finding the fixed differences between the header and body text.

This is why representatives of Polish government asked English and French intelligence for help, and in the conference 24th July 1939 they presented their allies with the plans of 'The Bomb' and the documentation detailing the required development of the decryption devices. English cryptanalysts in Bletchley Park, using the principles devised by Alan Turing managed to build the required device, although this happened only after the war already broke out.

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