In World War II, military leaders used wireless radio communication to pass military messages to troops all over the world. Unfortunately, radio messages could be intercepted. If enemy forces intercepted a message, they would have time to prepare for an attack.

To prevent the enemy from intercepting information, plans and orders were transmitted using secret codes. During World War II, the Germans invented a special machine called “Enigma” to encode their secret messages.

The Allies eventually cracked the German code, thanks to the work of Polish and British mathematicians. In the 1930s, a German traitor gave information to the Allies, which Polish cryptologists used to copy the Enigma machine and solve its letter-scrambling patterns. The Allies gave a special code name to information from decrypted Enigma messages: “ULTRA.”

Cryptologists also unlocked secret Japanese codes. By 1940, the U.S. Army and Navy could read diplomatic Japanese messages between Tokyo and embassies in London, Washington, Berlin and Rome.

Sadly, these diplomatic messages did not provide specific military information, so the United States had no advance knowledge of the planned Pearl Harbor attack on December 7, 1941.

Although cryptology played a key role in World War II, it had been used for centuries before then. In ancient times when important documents and military commands were carried on foot by messenger, kings and rulers would encrypt the letters they sent to troops and allies.

This ensured that information would remain secret if the messages were intercepted or stolen. Even George Washington sent secret messages to his troops and commanders.


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    • We think it’s COOL that you guys are learning about secret codes, Caleb’s Creek! We haven’t read that book yet, but now we will check it out! Thanks so much for suggesting it, and THANK YOU for visiting this Wonder of the Day®! :-)

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Have you ever wondered…

  • How do you break a secret code?
  • What is cryptology?
  • Why do people send secret messages?

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Try It Out

Did you know that codes can consist of any set of symbols used to represent something else? In fact, even regular words can be seen as codes.

For example, a code word for a four-wheeled vehicle is C-A-R. You understand this code, the alphabet, so you are able to understand the message!

Now it’s your turn to create a message in code. Need to send a message to an important friend? Find out how you can make a super-secret decoder wheel using paper plates.

Make one for a friend and one for yourself. When you’re finished, you can send super-secret messages back and forth!


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Today, you learned that secret codes were once used by armies to communicate important messages. Tomorrow, you’ll meet an instrument that also had a thing or two to say in wartime. Get ready to make beautiful music!

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