Codebreaking in World War I

Codebreaking in World War I

"The invention and use of radiotelegraphy, with the possibility of picking up anywhere at any time the radiations of a transmitter working at any point whatsoever, increased the possibility of interception in a way hitherto undreamed of. The hour when radiotelegraphy was born was also the hour of birth of illegal listening-in, i.e., of the so-called intercept service."

~ Wilhelm Flicke, The Beginnings of Radio Intercept in World War I

The use of radio prominently in World War I led to an increased focus on encrypting / ciphering messages to make them unreadable to enemies, as well as an increased focus on breaking these ciphers to read enemy messages.

Room 40 was located on the first floor on the first wing of this building. ​​​​​​​Photo courtesy of George Bell and Sons.

Britain's Room 40 was a codebreaking unit during the first World War that intercepted and deciphered tens of thousands of messages by hand.​​​​​​​​​​​​​​

The Zimmerman Telegram

"...Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona...The receipt of this information has so greatly exercised the British Government that they have lost no time in communicating it to you..."

Room 40 deciphered the Zimmerman telegram in 1917, a document sent by Germany to Mexico promising American territory in exchange for an alliance. This shocking discovery was forwarded to then US President Woodrow Wilson and helped push the US into World War, highlighting the impact that decrypted messages can have.

Codebreakers working in Room 40. June 1919. Photo courtesy of The History Press.

"In 1925 a file of over 10,000 sensitive highly secret decrypts from World War I Room 40 cryptanalysis were compromised in London to an American lawyer... Within weeks the German Army and German Foreign Office embarked on intensive and urgent programs to improve their cryptography." (Room 40 Compromise)

"The decrypts and associated lawsuit were widely publicized, and occupied the highest levels of the German government including Hitler and Goering, and the affair was cause celebre for over 12 years --- all because their cipher failures were exposed." (Room 40 Compromise)

German cryptographic failure in World War I greatly motivated Germany to upgrade its cryptography. In 1917, Arthur Scherbius was ordered to develop a cipher machine (Taaks). This would eventually lead to the creation of the Enigma machine.

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