Room 40

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In the history of cryptography, Room 40 (formally NID25) was the room in the Admiralty which was the first location of the British cryptography effort during World War I.

It was formed shortly after the start of the war in October 1914. Admiral Oliver, the Director of Naval Intelligence gave intercepts from the German radio station at Nauen near Berlin to Alfred Ewing the Director of Naval Education who constructed ciphers as a hobby. Ewing recruited civilians like William Montgomery, a translator of theological works from German and Nigel de Grey a publisher.

Then a German naval codebook and maps (containing coded squares) passed on to the Admiralty by the Russians who had seized them from the German cruiser Magdeburg when it had run aground. Two copies of the three which the warship had been carrying were recovered; one was retained by the Russians and the other passed to the British. A copy of a German Diplomatic codebook (for Code No 13040) was found in the baggage of Wilhelm Wassmuss from Persia.

Room 40 retained its informal name while it expanded during the war and moved into other offices. It closed in February 1919. It is estimated that Room 40 decrypted around 15,000 German communications. It was provided with copies of all interceptable communications traffic, including wireless and telegraph traffic. It was managed until May 1917 by Alfred Ewing, when direct control passed to Captain (later Admiral) Reginald 'Blinker' Hall^[1].

It played an important role in several naval engagements during the war, notably in detecting major German sorties into the North Sea that led to the battles of Dogger Bank and Jutland as the British fleet was sent out to intercept them. However probably its most important contribution was in decrypting the Zimmermann Telegram, a cable from the German Foreign Office to its ambassador Heinrich von Eckardt in Mexico.

In the cable's plaintext, Nigel de Grey and William Montgomery discovered German Foreign Minister Arthur Zimmermann making an offer to Mexico of United States territory as an enticement to join the war as a German ally. The cable was passed to the U.S. by Captain Hall, and a scheme was devised (involving a still unknown agent in Mexico and a burglary) to conceal how its plaintext had become available and also how the U.S. had gained possession of a copy. The cable was made public by the U.S., who shortly thereafter entered the war on the Allied side.

In 1919, Room 40 was run down and merged with the British Army's intelligence unit MI1b to form the Government Code and Cypher School (GCCS), later housed at Bletchley Park during World War II and subsequently renamed Government Communications Headquarters (GCHQ) and relocated to Cheltenham.

[edit] References

Patrick Beesly, Room 40: British Naval Intelligence, 1914-1918, New York: Harcourt, Brace, Jovanovich, 1982 ISBN 0-15-178634-8
The Zimmermann Telegram, by Barbara W. Tuchman, Ballantine Books, 1958 ISBN 0-345-32425-0
John Johnson, The Evolution of British Sigint: 1653–1939, 1997.