The Zimmermann Telegram (or Zimmermann Note) was a 1917 diplomatic proposal from the German Empire for Mexico to join an alliance with Germany in the event of the United States entering World War I against Germany. The proposal was intercepted and decoded by British intelligence. Revelation of the contents outraged American public opinion. President Woodrow Wilson moved to arm American merchant ships to defend themselves against German submarines, which had started to attack them. The news helped generate support for the United States declaration of war on Germany in April of that year.
The message came as a coded telegram dispatched by the Foreign Secretary of the German Empire, Arthur Zimmermann, on January 16, 1917. The message was sent to the German ambassador of Mexico, Heinrich von Eckardt. Zimmermann sent the telegram in anticipation of the resumption of unrestricted submarine warfare by Germany on 1 February, an act which Germany presumed would lead to war. The telegram instructed Ambassador Eckardt that if the U.S. appeared certain to enter the war, he was to approach the Mexican Government with a proposal for military alliance, with funding from Germany. As part of the alliance, Germany would assist Mexico to reconquer Texas and the Southwest. Eckardt was instructed to urge Mexico to help broker an alliance between Germany and Japan. Mexico, possessing far weaker armed forces than the U.S., ignored the proposal and after the U.S. entered the war, officially rejected it.
- FROM 2nd from London # 5747.
- "We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor in spite of this to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal of alliance on the following basis: make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona. The settlement in detail is left to you. You will inform the President of the above most secretly as soon as the outbreak of war with the United States of America is certain and add the suggestion that he should, on his own initiative, invite Japan to immediate adherence and at the same time mediate between Japan and ourselves. Please call the President's attention to the fact that the ruthless employment of our submarines now offers the prospect of compelling England in a few months to make peace." Signed, ZIMMERMANN
The Zimmermann Telegram was part of an effort that was being carried out by the Germans, in order to postpone the transportation of supplies and other war materials to the Triple Entente. The Zimmermann Telegram's main purpose was to make the Mexican government declare war on the U.S., which would have tied down U.S. forces and slowed the export of U.S. arms. The German High Command believed they would be able to use soldiers from the Eastern Front to defeat the British and French on the Western Front, and strangle Britain by unrestricted submarine warfare, before American forces could train and arrive in Europe in sufficient numbers.
Mexican President Venustiano Carranza assigned a military commission to assess the feasibility of a Mexican takeover of their former territories. The general concluded that it would not be possible or even desirable for the following reasons:
- The U.S. was far stronger than Mexico in its ability to make war. No serious scenarios existed under which Mexico could win.
- Germany's promises of "generous financial support" were far too good to be true. The German government had already informed to Carranza in June 1916 that they were unable to give the necessary gold in order to stock a completely independent Mexican national bank. Even if Mexico received the financial support, the arms, ammunition, and other needed war supplies would presumably have to be purchased from the ABC nations, especially Argentina, and this would strain relations as explained below.
- Even if by some chance Mexico had the military means to win the conflict with the U.S. and retake the area in question, Mexico would have had severe difficulty accommodating the large, primarily English-speaking population in that region who were better supplied than most populations with arms.
- Other foreign relations were at stake. The so-called ABC nations organized the Niagara Falls peace conference in 1914 to avoid a full-war between the US and Mexico over the United States occupation of Veracruz. If Mexico were to enter war against the U.S. it would strain relations with those nations.
Carranza government was de jure recognized by the United States on August 31, 1917, as a direct consequence of the Zimmermann telegram and in order to ensure Mexican Neutrality in WWI. After the military invasion of Veracruz in 1914, Mexico would not participate with the USA in its military excursion in WWI, so ensuring Mexican neutrality was the best deal, even when this neutrality allowed the German companies to keep their operations open in Mexico, especially in Mexico City.
The Telegram was sent to the German embassy in the U.S. for re-transmission to von Eckardt in Mexico. It has traditionally been claimed that the Telegram was sent by three routes: transmitted by radio, and also sent over two trans-Atlantic telegraph cables operated by neutral governments (the U.S. and Sweden) for the use of their diplomatic services. But it has been established that only one method was used. The message was delivered to the US Embassy in Berlin and then transmitted by diplomatic cable to Copenhagen and then to London for onward transmission over transatlantic cable to Washington. The disinformation about the 'three routes' was spread by W.R. Hall, the then head of Room 40, to try to shield from the USA the fact that Room 40 was intercepting its cable traffic.
Direct telegraph transmission was not possible because the British had cut the German cables in the Atlantic. However, the USA allowed a limited use of its diplomatic cables for Germany to communicate with its ambassador in Washington. The facility was supposed to be used for cables connected with President Woodrow Wilson's peace proposals.
The Swedish cable ran from Sweden; the U.S. cable from the U.S. embassy in Denmark. However, neither cable ran directly to the U.S. Both cables passed through a relay station at Porthcurno, near Land's End, the westernmost tip of England. Here the signals were boosted for the long trans-oceanic jump. All traffic through the Porthcurno relay was copied to British intelligence; in particular, to the codebreakers and analysts in Room 40 at the Admiralty. After their telegraph cables had been cut, the German Foreign Office appealed to the U.S. for use of their cable for diplomatic messages. President Wilson agreed to this, in the belief that such cooperation would sustain continued good relations with Germany, and that more efficient German-American diplomacy could assist Wilson's goal of a negotiated end to the war. The Germans handed in messages to the U.S. embassy in Berlin, which were relayed to the embassy in Denmark and then to the U.S. by American operators. However, the U.S. placed conditions on German usage—most notably, that all messages had to be in the clear. The Germans assumed that the U.S. cable was secure, and used it extensively.
At Room 40, Nigel de Grey partially deciphered the telegram by the next day. Room 40 had previously obtained German cipher documents, including the diplomatic cipher 13040 (captured in Mesopotamia), and naval cipher 0075, retrieved from the wrecked cruiser SMS Magdeburg by the Russians, who passed it to the British.
Disclosure of the Telegram would obviously sway U.S. public opinion against Germany, provided the Americans could be convinced it was genuine. But Room 40 chief "Blinker" Hall was reluctant to let it out, because the disclosure would expose Room 40's breaking of German codes, and also that Britain was eavesdropping on the U.S. cable. Hall waited three weeks. During this period, De Grey and William Montgomery completed the decryption. On 1 February Germany announced resumption of "unrestricted" submarine warfare, which led to the U.S. breaking off relations with Germany on 3 February.
Hall passed the telegram to the Foreign Office on 5 February, but still warned against releasing it. Meanwhile, the British discussed possible cover stories: to explain to the Americans how they got the ciphertext of the Telegram, without admitting to the cable snooping; and to explain how they got the cleartext of the Telegram without letting the Germans know their codes were broken. Furthermore, the British needed to find a way to convince the Americans the message was not a forgery.
For the first story, the British also got the ciphertext of the Telegram from the Mexican commercial telegraph office. The British knew that the German Embassy in Washington would relay the message by commercial telegraph, so the Mexican telegraph office would have the ciphertext. "Mr. H", a British agent in Mexico, bribed an employee of the commercial telegraph company for a copy of the message. (Sir Thomas Hohler, then British ambassador in Mexico, claimed to have been "Mr. H", or at least involved with the interception, in his autobiography.) This ciphertext could be shown to the Americans without embarrassment. Moreover, the retransmission was enciphered using cipher 13040, so by mid-February the British not only had the complete text, but also the ability to release the telegram without revealing the extent to which the latest German codes had been broken - at worst, the Germans might have realized that the 13040 code had been compromised, but weighed against the possibility of U.S. entry into the war that was a risk worth taking. Finally, since copies of the 13040 ciphertext would also have been deposited in the records of the American commercial telegraph, the British had the ability to prove the authenticity of the message to the U.S. government.
As a cover story, the British could publicly claim that their agents had stolen the Telegram's deciphered text in Mexico. Privately, the British needed to give the Americans the 13040 cipher so that the U.S. government could independently verify the authenticity of the message with their own commercial telegraphic records, however the Americans agreed to back the official cover story. The German Foreign Office refused to consider a possible code break, and instead sent von Eckardt on a witch-hunt for a traitor in the embassy in Mexico. (Von Eckardt indignantly rejected these accusations, and the Foreign Office eventually declared the embassy exonerated.)
British use of the Telegram
On 19 February, Hall showed the Telegram to Edward Bell, secretary of the U.S. Embassy in Britain. Bell was at first incredulous, thinking it was a forgery. Once Bell was convinced the message was genuine, he became enraged. On the 20th of February Hall informally sent a copy to U.S. ambassador Walter Page. On 23 February, Page met with British Foreign Minister Arthur Balfour, and was given the ciphertext, the message in German, and the English translation. Then Page reported the story to President Wilson, including details to be verified from telegraph company files in the U.S. Wilson released the text to the media on February 28, 1917.
Effect in the United States
Popular sentiment in the U.S. at that time was anti-Mexican as well as anti-German, while Mexico was anti-American. General "Black Jack" Pershing had long been chasing the revolutionary Pancho Villa, who had carried out several cross-border raids. News of the Telegram further inflamed tensions between the U.S. and Mexico.
On the other hand, there was also a notable anti-British sentiment in the U.S., particularly among German- and Irish-Americans. Many Americans wished to avoid the conflict in Europe. Since the public had been told (untruthfully) that the telegram had been stolen in a deciphered form in Mexico, at first the message was widely believed to be an elaborate forgery perpetrated by British intelligence. This belief, which was not restricted to pacifist and pro-German lobbies, was promoted by German and Mexican diplomats, and by some American papers, especially the Hearst press empire. This might have presented the Wilson administration with a dilemma—with the evidence the U.S. government had been confidentially provided by the British, Wilson quickly realized the message was genuine, but he could not make the evidence he had public without compromising the British codebreaking operation.
However, any doubts as to the authenticity of the telegram were removed by Arthur Zimmermann himself. First at a press conference on 3 March 1917, he told an American journalist, "I cannot deny it. It is true." Then, on 29 March 1917, Zimmermann gave a speech in which he admitted the telegram was genuine. Zimmermann hoped Americans would understand the idea was that Germany would only fund Mexico's war with the United States in the event of American entry into World War I.
On February 1, 1917, Germany began unrestricted submarine warfare against all ships in the Atlantic bearing the American flag, both passenger and merchant ships. Two ships were sunk in February, and most American shipping companies held their ships in port. Besides the highly provocative war proposal to Mexico, the Telegram also mentioned "ruthless employment of our submarines." Public opinion demanded action. Wilson had previously refused to assign US Navy crews and guns to the merchant ships. However, once the Zimmermann note was public, Wilson called for arming the merchant ships, but antiwar elements in the Senate blocked his proposal.
Previous German efforts to promote war
Germany had long sought to incite a war between Mexico and the U.S., which would have tied down American forces and slowed the export of American arms to the Allies. The Germans had engaged in a pattern of actively arming, funding and advising the Mexicans, as shown by the 1914 SS Ypiranga arms-shipping incident, and the presence of German advisors during the 1918 Battle of Ambos Nogales. The German Naval Intelligence officer Franz von Rintelen had attempted to incite a war between Mexico and the U.S. in 1915, giving Victoriano Huerta $12 million. The German saboteur Lothar Witzke—responsible for the March 1917 munitions explosion at the Mare Island Naval Shipyard in the Bay Area, and possibly responsible for the July 1916 Black Tom explosion in New Jersey—was based in Mexico City. The failure of U.S. troops to capture Pancho Villa in 1916, and the movement of President Carranza in favor of Germany, emboldened the Germans to send the Zimmermann Note.
Woodrow Wilson ordered the military invasion of Veracruz in 1914 in the context of the Ypiranga Incident. The occupation was a decisive factor in favor of keeping Mexican neutrality in World War I. Mexico granted full guaranties to the German companies for keeping their operations open, specifically in Mexico City. These guaranties lasted for 25 years—coincidentally, and on May 22, 1942, Mexico declared war on the Axis Powers following the loss of two Mexican-flagged tankers that month to Kriegsmarine U-boats.
In October 2005, the original British typescript of the deciphered Zimmermann Telegram was found.
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