zimmermann telegram

Room 40 and Zimmermann's Telegram

In early 1917, Germany was feeling the strangle of the British blockades. They needed to break the blockades and restore the supply train to German ports. Plans were made in 1916 to resume the use of unrestricted submarine warfare. The German High Command was aware that if they were to resume the sinking of vessels sailing from the United States it was likely that the US would enter into the war on the side of the Allies. However, it was assumed that it would take a considerable amount of time for American troops to be supplied, trained, and transported to the Western Front, by which time Germany could have knocked out France and forced England to peace talks. However, should the timetable be incorrect, the Germans wanted an insurance policy.

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Johann Heinrich von Bernstorff

On January 16th, the codebreakers in the British Admiralty in Room 40 received an intercepted communication transmitted over US diplomatic lines. German telegraph lines to the Americas had been severed at the beginning of the war and its stations in neutral countries shut down. As such it was forced to use British and American lines instead. German transmissions were generally sent along American lines which were kept open with the permission of American President Woodrow Wilson . He had given the German diplomats use of the lines as a way of keeping diplomatic channels open with the hope ending the war. The Germans took advantage of this privilege believing it offered them some degree of safety, as the British government couldn’t exploit any intercepted information without revealing that they were spying on American diplomatic traffic.

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Arthur Zimmermann

The intercepted message on January 16th was sent from the Berlin office of the German Foreign Secretary, Arthur Zimmermann to the German ambassador in Washington, Johann von Bernstaff. It was passed along quickly to the codebreakers who partially decoded it. The Germans had used their cipher 0075, which Room 40 had only partially decoded.

Earlier in the war, in 1914 the SMS Madgeburg had run aground in heavy fog while trying to evade Russian vessels. A majority of her codebooks and ciphers were destroyed, but many were retained for communication with rescuers. With the Russians closing in, Korvettenkapitän Richard Habenicht ordered her to be scuttled. With most of the Madgeburg’s crew rescued by friendly ships, the vessels trying to free her were driven off when Russian ships came close and began firing. In the confusion, many of the scuttling charges went off, killing fifteen men. Fifty six men as well as the captain were captured by the Russians, and the Madgeburg was seized. Inside, the Russians found two codebooks and later a cipher key that had been thrown overboard. After this the Madgeburg was completely destroyed and the codebooks and cipher were turned over to the British Admiralty and Rear Admiral Henry Oliverwho was the Director of Naval Intelligence.

With code 0075 partially broken the British were able to decipher enough of the message to ascertain its intent. It revealed a proposed alliance between Germany and Mexico and that Germany was to resume unrestricted submarine warfare on the 1st of February. Germany would supply Mexico with “generous financial support” if Mexico would declare war on the United States, thereby occupying American attention and allowing Germany to defeat the Allies in Europe. In return, Mexico would be given her “lost territory in Texas, New Mexico, and Arizona.” Further, it requested Mexican assistance in enlisting Japan into a similar agreement. It finished by informing Mexico that Germany’s renewed submarine efforts would force England to peace within a few months.

This information presented the British with a political conundrum. They wanted to utilize the information to stir public sentiment in the United States against Germany. However, they needed a way that would let them inform the American government without alerting them to the British spying on American diplomatic traffic, and further, they had to explain how they were able to decipher the text without admitting that they had broken the German’s code. They solved their first problem when a British agent in Mexico bribed an employee of the Mexican telegraph office for a copy of the telegram, which had been forwarded from Washington to Mexico via commercial lines. It had been encoded with the German cipher 13040, and the British had captured the complete copy of this cipher in Mesopotamia and it had been completely decoded by mid-February. When this was done, and the information of the telegram was relayed, the British lied, saying they had stolen a deciphered copy. Eventually the US was informed that they had broken the code, but the American government played along with the ruse. The German government, unable to accept that their codes could have been broken, sent von Eckardt to find who stolen the telegram. On February 23rd, the US Ambassador, Walter Page met with the British Foreign Minister Arthur Balfour and was given the ciphertext, the deciphered German version and the English translation. Page then relayed the information to Woodrow Wilson back in the US.

Prior to American involvement in the war, American General John J. Pershing had been leading the American effort against the Mexican revolutionary Pancho Villa. Villa had perpetrated multiple incursions and raids in the United States, the deadliest of which was against the New Mexican town of Columbus, which escalated into a full-scale battle between his forces and Pershing’s. In light of this conflict, American public sentiment was anti-Mexican as well as anti-German. When the telegram’s details were made public, there was outrage. However, at the same time there was a sizeable amount of anti-British sentiment at play and it was particularly notable in the Irish American and German American population. First and foremost Americans generally wished to avoid involvement in what they saw as just another European conflict. However, by February 1st, after Germany had resumed their practice of unrestricted submarine warfare, anti-German sentiment was rapidly overtaking the American people. With the publishing of the Zimmermann Telegram, these feelings were inflamed. The Telegram would, in part, help push the United States towards involvement in the First World War.