Enigma Machine

The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the German military. The Enigma machine was considered so secure that it was used to encipher the most top-secret messages... While Nazi Germany introduced a series of improvements to the Enigma over the years, and these hampered decryption efforts, they did not prevent Poland from cracking the machine prior to the war, enabling the Allies to exploit Enigma-enciphered messages as a major source of intelligence.[2] Many commentators say the flow of Ultra communications intelligence from the decryption of Enigma, Lorenz, and other ciphers, shortened the war substantially, and might even have altered its outcome. https://en.wikipedia.org/wiki/Enigma_machine

cf https://en.wikipedia.org/wiki/Signals_intelligence#World_War_II