In World War II, the Allies listened in to radio calls made by Hitler’s armed forces. His Generals thought no one could read their messages because they used secret codes. But the Allies cracked the codes, so knew what they were planning!
It was Polish mathematicians who first worked out how to crack the German codes. With help from the French resistance, they passed it on to the British. Prime Minister Winston Churchill then set up a secret team at Bletchley Park to do the code breaking. The team included Alan Turing, one of the greatest computer scientists ever. Together they made lots of code breaking breakthroughs.
The Germans used machines to encrypt their messages. Every day they changed the settings on the machines to make a new code. So the women and men at Bletchley had to crack the codes anew every day. The first computers were built to help them do this quickly each day so they could start to read the messages while the information was still useful.