Zimmermann Telegram

The Zimmermann Telegram was a telegram written to the government of Mexico by the foreign minister Arthur Zimmermann of the German Empire during World War One on January 16, 1917, proposing that Mexico ally itself with Germany if the United States were to enter the war. In it he suggested that, were Mexico to launch a pre-emptive strike on the United States, it would have Germany's backing and would be rewarded with Texas, New Mexico and Arizona if the war was won. It also urged Mexico to mediate between Germany and Japan, to convince the Japanese to enter the war against the US. Sent during a period of anti-German hype in the United States, following the loss of some two hundred Americans to German submarine attacks, the telegram was apparently intercepted and decrypted by the codebreakers of the British Naval Intelligence unit, Room 40, under Admiral William R. Hall.

The British government, which wanted to expose the incriminating telegram, faced a dilemma: If it exposed the actual telegram, the Germans would be led to suspect that their code was broken, and if it did not, it would lose an important opportunity to draw the United States into World War I. The British knew that there existed a Mexican decrypted version of the telegram, and that, if they could lay their hands on it, they could pretend that the telegram was obtained as a result of espionage activity in Mexico, and not as a result of code breaking. Therefore, the British government contacted a British agent in Mexico, known only as Mr. H., who managed to get a copy of the Mexican version of the telegram.

The telegram was delivered by Admiral Hall to the British Foreign Minister, Arthur James Balfour, who in turn invited the American ambassador in Britain, Walter Page, and delivered the telegram to him on February 23rd. Two days later he relayed it to President Woodrow Wilson.

American sentiment was generally as anti-Mexico as it was anti-German. General John J. Pershing had long been chasing Pancho Villa, who had been attacking inside Texas. This was a great expense to the government, and Wilson was leaning towards discontinuing the search until after new elections were held in Mexico, a new government installed, and a new constitution in place. News of the telegram exacerbated tensions between the U.S. and Mexico, since such a treaty, if in place, would have hindered the election of a new Mexican government more friendly to American interests.

On March 1, the US Government gave the plaintext of the telegram to the press. Although the telegram began by stating that Germany was most interested in maintaining American neutrality, its release to the public evoked an outpouring of anti-German sentiment. Wilson responded to this manifestation of German hostility by asking Congress to arm American ships so that they could fend off potential German attacks. One month later, on April 2, Wilson asked Congress to declare war on Germany. Four days later, on April 6, 1917, Congress complied, bringing the United States into World War I.

German submarines had previously attacked US ships near England, so the telegram was not the only cause of the war; it was, however, critical for US public opinion. It was perceived as especially perfidious that the telegram was first transferred from the US embassy in Berlin to the German embassy in Washington before being passed on to Mexico.

Although German, Mexican and Japanese diplomats, and the American pacifist and pro-German lobbies all denounced the telegram as a forgery, Zimmerman himself, in a startling move, confirmed its authenticity. After he had done so it became all but inevitable that the US would join the Great War.

The Zimmermann telegram as it was sent from the German ambassador in Washington to Mexico. Every word was encrypted into a four or five digit number, using a codebook.

The telegram as decrypted by the British Naval Intelligence codebreakers. The word Arizona was not in the German codebook and was therefore split into smaller parts.

The telegram, completely decrypted and translated.