The Zimmermann Telegram: The Message That Pulled America Into War A telegram in code groups, a broken cipher and a continent set alight: this guide walks the Zimmermann telegram from a Berlin desk to American front pages. Quick facts Author Arthur Zimmermann Sent 16 January 1917 Code 0075 groups Broken by Room 40 Published 1 March 1917 Room 40's handling of the intercept - sourcing a second copy in Mexico City so the method stayed hidden - remains a masterclass in using intelligence. The contents did the rest: within weeks, American opinion had swung behind war. Start now: Morsecodeworks.com Morse Code Works - free Morse code tools and guides. Reference chart