When World War I broke out, the United States stood on the side and decided it was a war not for it to wage. For two and a half years, the US remained a neutral country until, in 1917, things began to shift, and the country was being drawn into the conflict, especially when Germany declared its unrestricted submarine warfare that permitted the attacks of their U-boats to torpedo ships regardless of their military status and country of origin. The last straw was said to be a telegram sent by Germany to Mexico.
Germany’s Underground Works
Perhaps for the Germans, the best place to hide was right under their (future) enemy’s nose, so even before they declared unrestricted submarine warfare, they started their diplomatic scheme in motion through a secret letter sent by the German foreign secretary Arthur Zimmermann in 1917. The letter was intended for Heinrich von Eckardt, the German minister in Mexico. The note’s scandalous content stated his plan of negotiating a military partnership with Mexico if the United States entered the war on the side of the Allied forces. They would propose that Mexico would be free to annex a portion of the American Southwest territory in exchange for launching an attack on the US. Part of the letter said,
We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor despite 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.
Germany had lost its transatlantic telegraph cables earlier in the war when the British Royal Navy cut through them, leaving the Germans with no way of communicating privately between Berlin and North America. Still, the neutral United States agreed to send the letter on the condition that the contents were only diplomatic instructions and nothing more, unaware that its content was a threat to its security. On January 16, 1917, the telegram was handed to the US ambassador to Germany, James Gerard. He dutifully wired the letter to Copenhagen, where it was again transmitted to London and then to the German embassy in Washington. The letter reached Eckardt’s hands by January 19.
Intercepting the Zimmermann Telegram
Although the United States at that time was unaware of the whole thing happening behind its back, Britain wasn’t. Unknown to them, the British intelligence was secretly tapping into their transatlantic cables since the beginning of the war. So when the US transmitted the Zimmermann Telegram, a group of cryptographers, language experts, and mathematicians in an office called “Room 40” had the coded message intercepted and decoded that Britain already knew what was up two days before the telegram reached Washington. Nigel de Grey, a British cryptanalyst who cracked the letter, was remembered for the question he asked Captain William Reginald “Blinker” Hall after knowing the message. He asked, “Do you want to bring America into the war?”
It was not just a matter of a yes or no answer from Hall. Releasing the letter would reveal two things: First, that the German codes had been decoded, and second, that the British were eavesdropping on America’s diplomatic communications. He decided that he wanted to let the United States know about the plan, but in a way that would not reveal their underground work. He had a brilliant solution to the puzzle.
Revealing the Discovery
After Germany’s unrestricted submarine warfare began on February 1, President Wilson responded by severing diplomatic relations with Germany, still not dragging the country into the war, not until Hall revealed their scandalous discovery, but how did he manage to do it without exposing the source of information? He said that the intelligence was from a second copy of the Zimmermann Telegram after it had been sent from Washington to Mexico and that they intercepted it when it arrived in Mexico.
The full text of the telegram was published in American newspapers on March 1, 1917, and two days later, Arthur Zimmermann admitted that he indeed wrote the letter. At that time, Mexico had already rejected German’s offer, so Japan received the same proposal.
Wilson appeared before Congress on April 2, 1917, to ask for a declaration of war against Germany; one of the reasons that he cited was the Zimmermann Telegram.