The Enigma was a sophisticated German machine for the encryption of messages.
Drawing on Polish expertise and experience, the British first broke the German Navy's Enigma cipher in 1941. This allowed them to read many important messages and to help track the movements of German U-Boats (submarines). Enigma could not always be deciphered, however, because the Germans kept improving the equipment and changing its settings. The German Navy used this 1943 example.
Enigma Encryption Machine Type M4