Code Breakers!

Germany invaded Poland on September 1, 1939. This was a key step in dictator Adolf Hitler’s plan to conquer all of Europe. Two days later, the United Kingdom and France declared war on Germany. Over the next six years, the Allies, led by the U.K. and France—and later the U.S. and Soviet Union—battled the Axis powers of Nazi Germany, Italy, and Japan during World War II.

Early on, Germany seemed unstoppable. Nazi troops occupied France. Stealthy submarines blew up supply shipments from the U.S. Planes bombed London for eight months straight during the Blitz. But just 50 miles north of London, a top-secret project was underway. The country’s brightest minds gathered at an estate called Bletchley Park.

On September 1, 1939, Germany invaded Poland. German dictator Adolf Hitler planned to take over all of Europe. Two days later, the United Kingdom and France declared war on Germany. This was the beginning of World War II, which lasted for the next six years. The U.K., France, the U.S., and the Soviet Union teamed up to form the Allies. They battled the Axis powers of Nazi Germany, Italy, and Japan.

Early on, Germany seemed unstoppable. Nazi troops occupied France. When the U.S. tried to ship supplies, German submarines blew them up. Planes bombed London for eight months straight. But everything was about to change.

Their mission: decipher the Nazis’ top-secret encrypted messages. Hundreds of teenage girls worked there. Each played a key part in the painstaking process of code breaking. Candace Fleming’s book The Enigma Girls* tells the story of these young women. Read on to meet some teen girls from the book.  (*The Engima Girls was published by Scholastic, which also publishes Scholastic MATH)

Just 50 miles north of London, a secret project was underway. The setting: a countryside estate called Bletchley Park. The U.K government had gathered some of the brightest minds in the country there. Their mission: decipher the Nazis’ coded messages to each other.

Hundreds of teenage girls worked on the project. Each played a key part in the code breaking process. Candace Fleming’s book The Enigma Girls* tells the story of these young women. Read on to meet some of the girls from the book. (*The Engima Girls was published by Scholastic, which also publishes Scholastic MATH)

Jane’s job was to help decipher  messages from the German Navy and Air Force. Both used a device called the Enigma machine. It encrypted messages using a cipher, which is a system of secret writing in which every letter is changed. The Germans thought the ciphers made by Enigma machines were unbreakable. But were they?

Jane’s job was to help decode messages from the German military. The Germans encrypted them, or turned them into secret code, using a device called the Enigma machine. The Germans thought the Enigma machines’ codes were unbreakable. But were they?

Each Enigma machine has two keyboards. As a message is typed in the bottom one, encrypted letters light up on the top one. There are
159 quintillion,
or
159,000,000,000,000,000,000
possible settings for the Enigma!

Each Enigma machine has two keyboards. As a message is typed in the bottom one, encrypted letters light up on the top one. There are
159 quintillion,
or
159,000,000,000,000,000,000
possible settings for the Enigma!

Each day, the German High Command shared the top-secret settings for the Enigma machines with the troops. After updating the settings, a user typed their message. Each key press caused an encrypted letter to light up. Another person recorded the newly encrypted message, one letter at a time. Then they sent the encoded message over the radio. Whoever received the message needed to know the exact same Enigma settings to decrypt it. Anyone could listen in on the transmission—and they did—but the encrypted messages looked like gobbledygook! It took a lot of hard work to decipher the message (see How to Break a Cipher, below).

Enigma machines used ciphers to encrypt messages. A cipher is a system of secret writing where every letter is changed. Each day, German military leaders shared top-secret settings for the Enigma machines. Those settings determined how the letters in a coded message would change.

To encrypt a message, a user typed on the Enigma’s keyboard. Pressing a key lit up an encrypted letter on another part of the machine. Another person wrote down those letters. Then they sent the coded message over the radio.

Anyone could listen in on a radio transmission. But the encrypted messages looked like nonsense unless you knew the code. To decode a message, you needed to know the exact Enigma settings the Germans were using. And figuring that out took a lot of hard work. (see How to Break a Cipher, below).

The battleship Bismarck was the pride of the German Navy. It had been sinking U.S. supply ships as they crossed the North Atlantic. On May 24, 1941, the British ship HMS Hood battled with the Bismarck. The Hood broke in half and sank. The Bismarck was leaking fuel and taking on water. It needed repairs. But where would it go? France? Norway? There were too many options!

To catch the Bismarck, Jane and the rest of Bletchley Park’s staff raced to decipher its messages. Other teams had found the settings and Jane updated her own version of an Enigma machine. As she typed, Jane saw a name she recognized: Brest. This city in northwestern France was the perfect place for repairs. Jane ran to alert her supervisors. The message she deciphered was sent to British command, and hours later the navy found the Bismarck and sank it.

The battleship Bismarck was the pride of the German Navy. It had been sinking U.S. supply ships as they crossed the North Atlantic. The Allies wanted to destroy the Bismarck. But they would need to catch it first.

On May 24, 1941, a British ship battled with the Bismarck. The British ship lost the fight and sank. The Bismarck was left leaking fuel and taking on water. The British knew the Germans would need to dock it for repairs. But where would it go? France? Norway? There were too many options!

The Bismarck’s crew shared their plans in coded messages. Jane and the rest of the Bletchley Park staff raced to decipher them. Other teams had figured out the Enigma settings the Germans were using that day. Jane used those to update her own version of an Enigma machine. She typed in a coded message and watched decoded letters light up. She recognized the name of a city in northwestern France. It was the perfect place for repairs! Jane ran to tell her supervisors. The message was sent to British leaders. Hours later, the navy found the Bismarck and sank it. 

Intelligence from Bletchley Park was key to winning the war. It helped the Allies plan D-Day. In this historic operation, troops from the U.S., the U.K., and Canada invaded beaches along the northern coast of Nazi-occupied France. Seven months after D-Day, Germany surrendered. Japan fell five months later. World War II was over on September 2, 1945.

After the war, Bletchley Park shut down. The women disassembled the code breaking machines, burned the cards in the Index Room, and removed all evidence of their work. The site was abandoned by the military. The teen girls—now young women—returned to their regular lives. They found new jobs, got married, and never spoke of their experience. Jane became a famous opera singer!

It wasn’t until the 1990s that Bletchley Park’s role was revealed to the world. The women finally started speaking up about—and being recognized for—their contributions to winning World War II.

The work at Bletchley Park was key to winning the war. It helped the Allies plan the historic operation known as D-Day. Troops from the U.S., U.K., and Canada invaded the beaches of Nazi-occupied France. Seven months later, Germany surrendered. Five months later, Japan did too. On September 2, 1945, World War II was over.

After the war, Bletchley Park shut down. The staff took apart the code breaking machines. They destroyed all evidence of their work. The girls were now young women, and they returned to their regular lives. They found new jobs, got married, and never spoke about their experience. Jane became a famous opera singer!

The importance of Bletchley Park wasn’t revealed to the world until the 1990s. The women finally started speaking up about their work. At last, they could be recognized for what they did—and how much it helped with winning World War II.