Japanese and Italian models were also in use. Several different Enigma models were produced, but the German military models, having a plugboard, were the most complex. Early models were used commercially from the early 1920s, and adopted by military and government services of several countries, most notably Nazi Germany before and during World War II. The German firm Scherbius & Ritter, co-founded by Scherbius, patented ideas for a cipher machine in 1918 and began marketing the finished product under the brand name Enigma in 1923, initially targeted at commercial markets. This was unknown until 2003 when a paper by Karl de Leeuw was found that described in detail Scherbius' changes. The Enigma machine was invented by German engineer Arthur Scherbius at the end of World War I. Many commentators say the flow of Ultra communications intelligence from the decrypting of Enigma, Lorenz, and other ciphers shortened the war substantially and may even have altered its outcome.

Poland's sharing of her achievements enabled the western Allies to exploit Enigma-enciphered messages as a major source of intelligence. 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 as early as December 1932 and reading messages prior to and into the war. The receiving station would have to know and use the exact settings employed by the transmitting station to successfully decrypt a message. The security of the system depends on machine settings that were generally changed daily, based on secret key lists distributed in advance, and on other settings that were changed for each message. The rotor mechanism changes the electrical connections between the keys and the lights with each keypress. Entering ciphertext transforms it back into readable plaintext. If plain text is entered, the illuminated letters are the ciphertext. In typical use, one person enters text on the Enigma's keyboard and another person writes down which of the 26 lights above the keyboard illuminated at each key press. The Enigma has an electromechanical rotor mechanism that scrambles the 26 letters of the alphabet.

The Enigma machine was considered so secure that it was used to encipher the most top-secret messages. It was employed extensively by Nazi Germany during World War II, in all branches of the German military. The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication.

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