Polish Cipher Bureau

The Biuro Szyfrów ([ˈbʲurɔ ˈʂɨfruf], Polish for "Cipher Bureau") was the interwar Polish General Staff's Second Department's organizational unit charged with SIGINT and both cryptography (the use of ciphers and codes) and cryptanalysis (the study of ciphers and codes, particularly for the purpose of "breaking" them).

The precursor of the agency that would become the Cipher Bureau was created in May 1919, during the Polish-Soviet War (1919–21), and played a vital role in securing Poland's survival and victory in that war.

In mid-1931, the Cipher Bureau was formed by the merger of pre-existing agencies. In December 1932, the Bureau began breaking Germany's Enigma ciphers. Over the next seven years, Polish cryptologists overcame the growing structural and operating complexities of the plugboard-equipped Enigma. The Bureau also broke Soviet cryptography.

Five weeks before the outbreak of World War II, on 25 July 1939, in Warsaw, the Polish Cipher Bureau revealed its Enigma-decryption techniques and equipment to representatives of French and British military intelligence, which had been unable to make any headway against Enigma. This Polish intelligence-and-technology transfer would give the Allies an unprecedented advantage (Ultra) in their ultimately victorious prosecution of World War II.

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