The breaking of the German teleprinter cipher that led to the construction of the Colossus computer was the culmination of a series of triumphs for British codebreakers. British interception of other countries’ radio communications had begun in earnest during the First World War. The War Office ‘censored’ diplomatic communications passing through the hands of the international telegraph companies, setting up a codebreaking operation to decipher the secret messages. The British Army intercepted German military wireless communications with a great deal of success. E. W. B. Gill, one of the army officers involved in decoding the messages, recalled that ‘the orderly Teutonic mind was especially suited for devising schemes which any child could unravel’. One of the most notable successes for the British cryptanalysts came in December 1916 when the commander of the German Middle-East signals operation sent a drunken message to all his operators wishing them a Merry Christmas. With little other activity taking place over the Christmas period, the same isolated and clearly identical message was sent out in six different codes, only one of which, until this point, the British had managed to break. The army codebreaking operation became known as MI1b and was commanded by Major Malcolm Hay, a noted historian and eminent academic. It enjoyed a somewhat fractious relationship with its junior counterpart in the Admiralty, formally the Naval Intelligence Department 25 (NID25) but much better known as Room 40, after the office in the Old Admiralty Buildings in Whitehall that it occupied. The navy codebreaking organisation had an even more successful war than MI1b, recruiting a number of the future employees of Britain’s Second World War codebreaking centre at Bletchley Park, including Dillwyn ‘Dilly’ Knox, Frank Birch, Nigel de Grey, and Alastair Denniston, who by the end of the war was head of Room 40. Among the many successes of the Royal Navy codebreakers was the breaking of the Zimmermann telegram, which showed that Germany had asked Mexico to join an alliance against the United States, offering Mexico’s ‘lost territory’ in Texas, New Mexico, and Arizona in return, and brought the United States into the war.