Below is a copy of the famous telegram that was sent by German's Foreign Minister Arthur Zimmermann in World War I. It was sent to the Mexican President. Zimmermann asked for Mexico's help in case the USA would be involved in the war and suggested to "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. The settlement in detail is left to you." The message was encrypted as you can see, but was cracked by the people of "Room 40", the British Admiralty's cipher bureau. Both the original message and the decoded one are displayed below.
Pictures source: http://www.archives.gov
Gretag AG TC-53
A hardcopy from the old days. M29 'VDE' copied on 17 February 1986 at 22.15 UTC.
Equipment used: FRG7700, Commodore 64 and a UG24 Microlog SWL/Airdisk decoder.