Room 40
In August 1914, British cable ship Telconia entered the North Sea and the men on-board cut the transatlantic cables and hence cut-off Germany from communicating through wired lines to the rest of the Western Europe and USA (Kahn, 1967). This forced Germany to use radio for all communication or use cables controlled by the Allies and hence allowed the Allies to intercept. In contrast, the British and French used wireless to communicate with ships at sea and not otherwise.
But Britain had no formal codebreaking organization even though intercepts were piling up. The Director of Naval Education, Alfred Ewing, put together a team of mostly volunteers from naval colleges to work on the intercepts. But they made no real progress. It was in September 1914 that the German cruiser Megdeburg was wrecked in Baltic and the Russians were able to obtain two cipher and signalling books from a drowning German officer. The Russians gave one of the books to the British. But Ewing’s team could not find any correlation between the four letter words in the books and the intercepts. Later it was found that the code had been superenciphered by monoalphabetic substitution. With the codebook in possession, deciphering became easy. Some codewords appeared more frequently, allowing for frequency analysis. Also the consonants appeared alternately with the vowels in the German codewords. The British acquired two more codebooks, one from a German-Australian steamer, Hobart, and another from the sinking German destroyer SMS S119 in the battle of Texel Island. With increasing number of intercepts and more men being recruited to decipher them, Ewing’s team moved to a large room Room 40, which lead to the organization informally being called Room 40.
Most intercepted messages reported the whereabouts of Allied ships. Though interesting, this information was not vital to the British. They recognized that the Germans also used short wave which the British could not intercept with the available infrastructure. So a station was set up to monitor shortwave signals and information about the movements of the High seas fleet was obtained. Even though it was no secret that the British had access to the codebook, the German’s continued to use the same until mid-1916. The book was massive and it could not be easily changed. But they did increase the frequency of changing the keys for monoalphabetic substitution. At the beginning of the war, the key was changed once in 3 months. In 1916, it was changed every midnight. But Room 40 had developed expertise and only needed few hours to find the new key every day.
Room 40 played an important role throughout the war. Winston Churchill wrote, “Without the cryptographers’ department there would have been no Battle of Jutland”. But the most important contribution of Room 40 was to decipher the Zimmerman telegram in 1917 which lead to America’s entry in the war. In this telegram, the German Foreign Minister Arthur Zimmerman offered Mexico the territories of Texas and Arizona if they join the war as a German ally. The message was sent from the US embassy in Berlin through Copenhagen and London to the German embassy in Washington. It was to be retransmitted to Mexico from there. The message read as follows:
We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor in spite of this to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal of alliance on the following basis:Make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona. The settlement in detail is left to you. You will inform the President [of Mexico] of the above most secretly as soon as the outbreak of war with the United States of America is certain and add the suggestion that he should, on his own initiative, invite Japan to immediate adherence and at the same time mediate between Japan and ourselves. Please call the President’s attention to the fact that the ruthless employment of our submarines now offers the prospect of compelling England in a few months to make peace.
Zimmerman
Reference:
Kahn, David (1967), The Code Breakers: The Story of Secret Writing, Weidenfeld and Nicolson
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