Telegram that brought US into Great War is found
It was intercepted and deciphered by Room 40, a predecessor of GCHQ, the Government's top secret listening post, in January 1917.
So many documents surrounding the affair were destroyed on the orders of Adml Sir Reginald "Blinker" Hall, the director of naval intelligence, it was assumed the original typed "decrypt" was gone for ever. But the official historian of GCHQ found it while researching an "official", that is to say secret, history of the organisation.
"It is a chance survival," said the historian, who asked not to be named. "It is thrilling to have got it."
The interception of the Zimmerman Telegram gave Britain the lever it needed to drag America into the war which had fallen into stalemate on the Western Front.
The decrypted message showed Arthur Zimmerman, the German foreign minister, instructing his representative in Mexico City to persuade the Mexicans to invade America.
In exchange, Germany would guarantee the "reconquest" of Texas, New Mexico and Arizona, lost by Mexico to America 70 years earlier.