Cipher Department of the High Command of the Wehrmacht

The Cipher Department of the High Command of the Wehrmacht (German: Amtsgruppe Wehrmachtnachrichtenverbindungen, Abteilung Chiffrierwesen) (also Oberkommando der Wehrmacht Chiffrierabteilung or Chiffrierabteilung of the High Command of the Wehrmacht or Chiffrierabteilung of the OKW or OKW/Chi or Chi) was the Signal Intelligence Agency of the Supreme Command of the Armed Forces of the German Armed Forces before and during World War II. OKW/Chi, within the formal order of battle hierarchy OKW/WFsT/Ag WNV/Chi, dealt with the cryptanalysis and deciphering of enemy and neutral states' message traffic and security control of its own key processes and machinery, such as the rotor cipher machine ENIGMA machine. It was the successor to the former Chi bureau (German: Chiffrierstelle) of the Reichswehr Ministry.

The letter "Chi" for the Chiffrierabteilung is, contrary to what one might expect, not the Greek letter Chi, nor anything to do with the chi test, a common cryptographic test used as part of deciphering of enciphered message, and invented by Solomon Kullback, but only to the first three letters of the word Chiffrierabteilung (English:cipher department).

From the early 1930s to the start of the war, Germany (Weimar Republic), has a good understanding, and indeed a lead in both cryptoanalytic and cryptographic cryptology services. The various agencies had cracked the French–English inter-allied cipher, the Germans with some help from the Italian Communications Intelligence Organization stole American diplomatic codes, and codes taken from the British embassy in Rome, that enabled the breaking of the cipher, leading to some gains early in the war. Although the Germans worked to ensure its cryptologic services were effective at the outbreak of the war, the service offerings fragmented considerably among the German armed forces. OKW/Chi had jurisdiction over the entire military cryptologic bureaus, chairing the executive committee, for a number of reasons including increased specialisms for specific military tasks against opposing forces of a similar type, the inherent independence of agencies, and agencies vying for power and favour from Hitler, it was inevitable that the three military branches of German forces operated independently.

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