Who Broke the Wartime Codes?

Who Broke the Wartime Codes? — page 5 — WHAT WERE WARTIME CODES Codes and ciphers have been used since ancient times We know of secret codes used by the ancient Egyptians Greeks and Romans The oldest known military cipher was the scytale which dates back at least 2,500 years Imagine a long piece of leather or papyrus which is wrapped around a piece of wood A message is written on the leather along the length of the wood Then the leather strip is unwound It contains a meaningless jumble of letters until it is wound around a piece of wood of exactly the same width when the message is suddenly revealed The advantages of not giving away your plans to your enemy were also well understood by the ancient Roman military leader Julius Caesar The Caesar cipher substituted letters by shifting the whole alphabet along often by three places So a became d b became e and so on We know about this cipher and about the scytale from descriptions by ancient writers HISTORY DETECTIVES WHAT IS A PRIMARY SOURCE The Zimmermann telegram see page 7 is an example of a

Who Broke the Wartime Codes? — page 6 — primary source a document that was written at the time being studied It gives us firsthand information about an event or a period in time Primary sources come in many different forms eyewitness accounts sketches or paintings documents such as wills or telegrams or from more recent times photographs or films You can find out more the Zimmermann telegram at www ourdocuments gov doc php flash true doc 60 THE ZIMMERMANN TELEGRAM We are now going to jump to the early 20th century and a room in London England for the next example of wartime code-breaking In this case the interception and deciphering of a telegram changed the course of a war Room 40 was the name given to the code-breaking section of the British Royal Navy set up in October 1914 just after the outbreak of World War I 1914 1918 In January 1917 the code-breakers of Room 40 worked on the text of a telegram sent by the German foreign minister Arthur Zimmermann to the German ambassador in Mexico At this point the United States had not entered the war although the Allies were becoming increasingly desperate for U S assistance In his telegram Zimmermann instructed the ambassador to suggest that Mexico join the war as a German ally In return Germany would ensure that the U S states of Arizona New Mexico and Texas would become Mexican territory

Who Broke the Wartime Codes? — page 7 — This is the coded text of the Zimmermann telegram written by the German foreign minister Arthur Zimmermann to the German ambassador in Mexico in 1917 The full text of the telegram was published in the U S press on March 1 1917 Zimmermann himself admitted that he had written it The impact on American public opinion was immediate and just over a month later on April 6 1917 the U S Congress declared war on Germany and its allies A NEW MACHINE From World War I onward a new technology sending

Who Broke the Wartime Codes? — page 8 — messages by radio required new levels and techniques of secrecy In 1918 a Swiss businessman Arthur Scherbius invented a machine to encrypt turn into cipher messages He sold it to banks and businesses as a security tool and called the machine Enigma The German armed forces began to use a military version of Enigma in 1926 So Enigma was not just one machine it was a type of machine and many Enigma machines were manufactured over the following decades SETTING THE SCENE It is important to remember that all the events described in this book happened before the computer age when the main forms of communication were radio and telephones with landlines and all records had to be kept on paper HOW DID ENIGMA WORK The Germans believed their Enigma ciphers were uncrackable They continued to believe this throughout World War II The British and Americans were incredibly careful about how they used intelligence gained from deciphered Enigma codes in order to keep the Germans using Enigma What was it about this machine that gave the Germans such faith Scherbius’s machine looked a bit like a typewriter with a keyboard When the operator pressed a letter on the keyboard the action moved rotors called scramblers Once a letter was

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