The Black Code (more formally, Military Intelligence Code No. 11) was a secret code used by US

military attachés A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...

in the early period of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. The nickname derived from the color of the

superencipherment Multiple encryption is the process of encrypting an already encrypted message one or more times, either using the same or a different algorithm. It is also known as cascade encryption, cascade ciphering, multiple encryption, and superencipherment. ...

tables/

codebook A codebook is a type of document used for gathering and storing cryptography codes. Originally codebooks were often literally , but today codebook is a byword for the complete record of a series of codes, regardless of physical format. Cryptog ...

binding. The code was compromised by

Axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...

intelligence, the information leak costing a great many British lives.

Theft of the Black Code

Unknown to the U.S. government, details of the Black code were stolen from the U.S. embassy in

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...

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. However, the limited information still assisted the Germans in their own independent efforts and they too were able to crack the Black Code. Beginning in mid-December 1941 Germany was able to read the reports of

Bonner Fellers Brigadier General Bonner Frank Fellers (February 7, 1896 – October 7, 1973) was a United States Army officer who served during World War II as a military attaché and director of psychological warfare. He is notable as the military attaché in ...

, U.S. military attaché in Cairo.Jenner, pp. 170 & 199 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 The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

, 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 Johannes Erwin Eugen Rommel () (15 November 1891 – 14 October 1944) was a German field marshal during World War II. Popularly known as the Desert Fox (, ), he served in the ''Wehrmacht'' (armed forces) of Nazi Germany, as well as servi ...

, 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". In June 1942 the British informed Washington that the "Cairo Code" was compromised and the U.S. Army

Signals Intelligence Service The Signal Intelligence Service (SIS) was the United States Army codebreaking division through World War II. It was founded in 1930 to compile codes for the Army. It was renamed the Signal Security Agency in 1943, and in September 1945, became th ...

promptly sent a

SIGABA In the history of cryptography, the ECM Mark II was a cipher machine used by the United States for message encryption from World War II until the 1950s. The machine was also known as the SIGABA or Converter M-134 by the Army, or CSP-888/889 by the ...

machine to Cairo. The leak ended on June 29, when Fellers switched to the new U.S. code system. But some, like Colonel

Alfred McCormack Colonel Alfred McCormack, CBE (1901-1956), was a trained attorney of Cravath, Swaine & Moore who during and after World War II served in the US Military Intelligence Service, where he proved crucial in developing military analysis of cryptographic ...

, were unconvinced and suspected that the British were reading the dispatches in the American "Black" code, not the Germans. McCormack finally concluded that was not the case, but considerable ill feeling had been aroused (Churchill had told Roosevelt in February 1942 that he had stopped British work on American diplomatic codes, a warning to tighten them up). Meanwhile, the Allies benefited from reports by Japanese attachés in Germany and by Ambassador

Hiroshi Ōshima Baron was a general in the Imperial Japanese Army, Japanese ambassador to Germany before and during World War II and (unwittingly) a major source of communications intelligence for the Allies. His role was perhaps best summed up by General Geo ...

References

{{reflist Military intelligence Signals intelligence of World War II Broken stream ciphers