During the time of World War I, almost all major undersea cables belonged
to the British, thus giving them all the copies of the contents that went
through them. Because the
British ship Telconia had cut the Germany’s few communication cables on
the first day of war, Zimmermann had no choice but to send it through
British cables. To secure the
contents of the telegram, Zimmermann en
crypted it, but did not realize the
skills of the British code breakers.
On January 17, 1917, the British Admiralty’s code-breaking office, Room 40, received a copy of a telegram that interested Nigel de Gray, a thirty-one year old publisher, and Reverend William Montgomery, a forty-six year old scholar, because of its unique length. They started to decrypt the material right away using printed German codebooks retrieved from sunken German ships.
As
they deciphered the telegram, they realized the message was in two parts,
one to Count von Bernstorff, the German Ambassador in Washington, and
another to the Imperial Minister in Mexico. After five weeks, the message
was fully deciphered to explain a future alliance between Germany, Mexico,
and Japan and encourage Mexico to plan a preemptive attack against the US
with the support of Germany. Mexico would be rewarded with
Texas, New
Mexico, and Arizona if the plan succeeded.
. This was a magnificent discovery for the British for they desperately needed aid from the United States, a powerful country. France, Britain and Germany had been in war for three years and both sides were rapidly losing great amounts of soldiers without much progress. Britain finally had an excuse for America to join the war. The next question was how they would warn America without revealing themselves to Germany.