Naval History and Heritage Command

Naval History and Heritage Command

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  • World War I 1917-1918
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H-002-1: Zimmerman Telegram 

H-Gram 002, Attachment 1
Samuel J. Cox, Director NHHC
29 December 2016 

In the first days of WWI, the British successfully executed a rather audacious plan (first formulated in 1911) to use a cable ship to cut German trans-oceanic cables close to their source off Germany, in order to force the Germans onto wireless or other paths that could be intercepted.  As a result, German diplomatic communications from Berlin to their embassy in Washington DC, with the agreement of the neutral U.S., were passed to the U.S. Embassy in Berlin, which forwarded the traffic via the U.S. diplomatic cable to Washington. This cable went via a relay station in England, which was monitored by British Naval Intelligence, unbeknownst to the U.S. or Germany.  A U.S. caveat was that German diplomatic traffic on this cable was to be passed in the clear, however, in the case of the Zimmerman telegram, the Germans convinced the U.S. Ambassador to pass it in code without informing him of the content.  By this time of the war, British Naval Intelligence could break several German codes (so could British Military Intelligence, but cooperation between the two was extremely strained) including the new code used for the Zimmerman telegram.  The success of British code-breaking was the result of multiple fortuitous events, of which one of the most significant was the grounding of the German light cruiser Magdeburg in the early days of the war off Russian-occupied Estonia, and the resulting Russian capture and sharing of several German code books.

The Director of Naval Intelligence, Captain Reginald Hall, initially did not want to release the contents of the telegram to the United States, fearing (rightly) that it would end up in the public domain.  Doing so would present the British with three major problems;

- 1. Keep the Germans from learning that their codes had been broken.

- 2. Keep the U.S. from learning that our diplomatic cable was being monitored

- 3. Convince the U.S. that the telegram was genuine.

To solve these problems, British Intelligence ran an operation in Mexico to bribe a commercial telegraph company employee to provide a copy of the coded telegram (the transmission from the German Embassy in Washington to Mexico City was in an older code that the British were prepared to "sacrifice" for the greater good of getting the Americans in the war on their side).  The British also provided details of the older code to the U.S., so that the U.S. could locate the message in the U.S. commercial company records and verify the authenticity of the message.   However, when the message was released to the public, the British and the U.S. used a cover story that a British agent had stolen a clear-text version in Mexico (providing the first spark for the decades of conspiracy theories.)  Zimmerman himself also (somewhat inexplicably) admitted in a public press conference with American journalists on 3 Mar 1917 that the telegram was authentic, which even though it was true, only further fueled the doubters. 

The public release was the first the Mexican government knew of the proposal, and President Carranza formed a military commission to study the details, which concluded that it would not be possible or desirable to invade the U.S. (among other things citing that the U.S. populations was "better supplied with arms than most populations.")  Nevertheless, anti-American sentiment in Mexico was very high, stemming from General Pershing's cross-border campaigns against bandit/”freedom fighter” Pancho Villa, multiple U.S. violations of Mexican sovereignty during the protracted Mexican Civil War, and especially the major U.S. Navy intervention at Vera Cruz in 1914.  As a result, German agents and military advisors had a significant presence in Mexico well before the Zimmerman telegram, and these agents would conduct some spectacular sabotage in the U.S. after the U.S. entered the war. Nevertheless, Mexico opted to sit out the First World War.  Mexico did join on the Allied side in WWII in March 1942 after Nazi German U-boats sank two Mexican tankers in the Gulf of Mexico. 

As an aside, Captain William Reginald Hall (nicknamed "blinker" due to a nervous facial twitch) became the Director of Royal Navy Intelligence in WWI after health issues resulted in him relinquishing command of the battle cruiser HMS Queen Mary (later sunk at Jutland with almost all hands).  While in command of the Queen Mary, Hall instituted a number of "firsts" (in any Navy), including the first "three section" watch (previously had been 12/12), the first shipboard chapel, first shipboard washing machines, and first shipboard movie projection capability, which led him to being accused by contemporaries of "coddling" his crew.   Hall proved to be extraordinarily capable and innovative in his role as Director of Naval Intelligence as well, promoted to Rear Admiral in 1917, and ultimately full-Admiral on the retired list in 1926.

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Published: Tue May 07 16:55:07 EDT 2019