Cryptography was used extensively during World War II, with a plethora of code and cipher systems fielded by the nations involved. In addition, the theoretical and practical aspects of cryptanalysis, or codebreaking, was much advanced.
Probably the most important cryptographic event of the war was the successful decryption by the Allies of the German “Enigma” Cipher. The first complete break into Enigma was accomplished by Poland around 1932; the techniques and insights used were passed to the French and British Allies just before the outbreak of the War in 1939. They were substantially improved by British efforts at the Bletchley Park research station during the War. Decryption of the Enigma Cipher allowed the Allies to read important parts of German radio traffic on important networks and was an invaluable source of military intelligence throughout the War. Intelligence from this source (and other high level sources, including the Fish cyphers) was eventually called Ultra.
A similar break into an important Japanese cypher (PURPLE) by the US Army Signals Intelligence Service started before the US entered the War. Product from this source was called MAGIC. It was the highest security Japanese diplomatic cypher.
Note worthy points back in history of code & ciphers :
Enigma : An Enigma machine is any of a family of related electro-mechanical rotor cipher machines used for the encryption and decryption of secret messages. Enigma was invented by German engineer Arthur Scherbius at the end of World War I.
Bergofsky ‘s Principle : the idea that if a computer tried enough keys, it is mathematically guaranteed to find the “right” one.
Bigglemans Safe: a hypothetical crypotgraphy scenerio in which a safe builder wrote blueprints for an unbreakable safe. He wanted to keep the blueprints a secret, so he built the safe and locked the blueprints inside.