So has Mexico.
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No study of codes and ciphers would be complete without a quick look at the famous German “Zimmerman” telegram. In short, Germany proposed a military alliance with Mexico; if she joined, Mexico could “regain” its lost territories from the United States. The Kaiser and the German High Command agreed and Germany sent a two-part telegram to its Embassy in Mexico City. Germany used a code system it numbered as “0075”. This system contained upwards of 10.000 phrases and individual words. One codebook was required to transmit the message, another book to decode a message. Secure enough, the Germans thought.
But Britain had an ace up its sleeve - Room 40 OB (Old Block) and Captain William Hall. In short, Captain Hall and his staff worked hard and decoded the Zimmerman telegram and the rest is now history.
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From the letter:
Berlin, January 19, 1917
On the first of February we intend to begin submarine warfare unrestricted. In spite of this, it is our intention to endeavor to keep neutral the United States of America.
If this attempt is not successful, we propose an alliance on the following basis with Mexico: That we shall make war together and together make peace. We shall give general financial support, and it is understood that Mexico is to reconquer the lost territory in New Mexico, Texas, and Arizona. The details are left to you for settlement....
You are instructed to inform the President of Mexico of the above in the greatest confidence as soon as it is certain that there will be an outbreak of war with the United States and suggest that the President of Mexico, on his own initiative, should communicate with Japan suggesting adherence at once to this plan; at the same time, offer to mediate between Germany and Japan.
Please call to the attention of the President of Mexico that the employment of ruthless submarine warfare now promises to compel England to make peace in a few months.
Zimmerman (Secretary of State)
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