Black (code)

The Black Code was a US secret code used by US military attachés in the early period of World War II prior to the entry of the United States. The name derived from the colour of the superencipherment tables/codebook binding. ^[1] The code was compromised by Axis intelligence, the information leak costing a great many British lives.

Theft of the Black Code

Unknown to the U.S. government, the details of the Black code were stolen from the U.S. embassy in Italy by Italian spies in September 1941. Embassy worker Loris Gherardi took copies of the embassy keys. These were passed on to the Italian Military Intelligence Service, who were able to break in, copy, and replace the documents.

The Italians did not pass on the full code to the Chiffrierabteilung, their German counterparts, only providing limited information such as decoded American messages.^[2] However the limited information still assisted the Germans in their own independent efforts and they too were able to crack the Black Code.^[2] Beginning in mid-December 1941 Germany was able to read the reports of Bonner Fellers, US military attaché in Cairo.^[3]

Fellers' radiograms provided detailed information about troop movements and equipment to the Axis. The information was extensive and timely to the Axis powers. Information from Fellers' messages alerted the Axis to British convoy operations in the Mediterranean Sea, including efforts to resupply the garrison of Malta. Beginning in January 1942 information about the numbers and condition of British forces was provided to General Erwin Rommel, the German commander in Africa. He could thus plan his operations with reliable knowledge about the opposing forces. The Germans referred to Fellers as "die gute Quelle" (the good source). Rommel referred to him as "the little fellow".^[2]

The information leak lasted until June 29, 1942, when Fellers switched to a newly adopted U.S. code system.^[3]

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