was the main French diplomatic cipher. Germany and Austria-Hungary The Imperial German Army and the Austro-Hungarian Army intercepted Russian radio communications traffic, although German success at the Battle of Tannenberg (1914) was due to interception of messages between the Imperial Russian Army commanders in cleartext. The German Abhorchdienst, a code-breaking bureau composed mainly of mathematicians, was established in 1916. The Germans had specific regulations regarding which kinds of codes and ciphers could be used under given circumstances. Within three kilometers of the front lines, known as the danger zone, all communications were required to be in a code known as the three-number code. This was the only code or cipher permitted. Behind this danger zone, another code known as the three-letter code was allowed to be used. Communications between divisions, corps, and army headquarters were done with the ADFGVX cipher. The ADFGX and ADFGVX field ciphers were a modified polybius system with single order double columnar transposition and frequent key change, with letters optimized for Morse. It was later broken by the famous French cryptanalyst Georges Painvin. The breaking of the ADFGX cipher by Painvin was the second time during the war that cryptanalysis played a major role in shaping events (the first being the interception and cracking of the Zimmerman Telegram). By breaking the cipher, the French were able to decode an intercepted message about the forwarding of munitions for a German offensive, letting the French know where and when the offensive would occur, and thus allowing them to stop it. This message became known as "The Radiogram of Victory." United States Herbert Yardley began as a code clerk in the State Department. After the outbreak of war he became the head of the cryptographic section of Military Intelligence Section (MI-8) and was with the American Expeditionary Force in World War I as a Signals Corps cryptologic officer in France. He later headed the Cipher Bureau, a new cryptanalysis group started in 1919, immediately after World War I, and funded jointly by the State Department and the US Army. Some American cryptography in World War I was done at the Riverbank Laboratories, Chicago, which was privately owned by Colonel George Fabyan. Elizebeth Friedman, William F. Friedman and Agnes Meyer Driscoll worked there. The US Navy used the cryptographic code A-1. The US Navy cryptanalysis group, OP-20-G, was also started after World War I (in 1922). The US also started