On November 21st, Keith Drinkwater presented the second of his cryptographic talks, entitled ‘The Zimmerman Telegram’.

This was an exciting tale about the decryption of encoded German telegram messages. The early destruction by the UK in 1914 of Germany’s undersea transatlantic cables and of their powerful radio stations made it necessary for Germany to use the UK/USA cable to send transatlantic messages. In 1917 German Foreign Secretary Arthur Zimmerman sent an encrypted message to Mexico’s Government which was intended to cause Mexico to declare war on the US, hindering them in their support of the Allies in WW1.

Room 40 in The Admiralty in London (a precursor of Bletchley Park in WW2) contained a couple of enthusiastic decoders who were able to take advantage of having a couple of different codebooks captured from the Germans to decode the Zimmerman telegram. Telling the US government its contents, without revealing their source to either US or Germans, brought USA into WW1 and the Germans were defeated 15 months later.