Lucky Break: the Zimmermann Telegram

David Nicholas reveals the skill and good fortune behind Britain’s First World War intelligence operation, and the coup by which the Zimmermann Telegram was cracked, tipping the balance in getting the US to join the Allied war effort.

The Zimmermann Telegram It is well known that the Second World War was significantly shortened thanks to the team at Bletchley Park, Milton Keynes, who cracked the code of the German Enigma machine, enabling the British to overcome the devastating U-boat campaign in the Atlantic. But fewer are aware of the Royal Navy’s huge success during the First World War in reading German naval codes. At the start of the war, the Germans were operating three military codes. Within four months, the British were in possession of all of them.

The science of reading enemy radio signals got started in a small room in the Admiralty, on the same corridor as the First Sea Lord’s office. Room 40 was 24 ft by 17 ft and looked out on the inner courtyard, remote from the rest of the Admiralty. Over the course of the First World War, some 20,000 German messages were decoded by Room 40, the name by which the operation continued to be known even after the unit expanded beyond its four walls.

Just hours after war was declared, the British assigned the cable ship, Telconia, to cut the first of five German cables, which ran from Emden, on the German-Dutch frontier, down the English Channel to France, Spain, Africa and the Mediterranean: a coup which forced the Germans to rely heavily on encoded wireless transmissions.

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