This Enigma machine was used by the German military during World War II to encode wireless messages ULTRA SECRET These are just two episodes in the secret world of code-breaking in World War II Of course all sides used codes and all were trying to break each other’s codes This book however mainly examines the work of the Allied code-breakers in the two most
significant operations The first of these was Ultra the name given to information obtained from the messages intercepted and deciphered by the British The second was Magic which was information gained by American code-breakers by intercepting and unscrambling Japanese signals The huge value of both operations was that Germany Italy and Japan remained unaware that their codes were being broken The name Ultra suggests this it was considered even more secret than top secret This was important and as we will see the Allies went to huge lengths to disguise and protect their code-breaking activities
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
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
