The Enigma machine was a cipher machine used to encrypt and decrypt secret messages. More precisely, Enigma was a family of related electro-mechanical rotor machines, comprising a variety of different models.
The Enigma was used commercially from the early 1920s on, and was also adopted by the military and governmental services of a number of nations—most famously by Nazi Germany before and during World War II.
The German military model, the Wehrmacht Enigma, is the version most commonly discussed. The machine has gained notoriety because Allies of World War II cryptologists were able to decrypt a large number of messages that had been enciphered on the machine. Decryption was made possible in 1932 by Polish cryptographers Marian Rejewski, Jerzy Różycki and Henryk Zygalski from Biuro Szyfrów (Cipher Bureau]. In mid-1939 reconstruction and decryption methods were delivered from Poland to United Kingdom and France. The Military intelligence gained through this source, codenamed ULTRA, was a significant aid to the Allied war effort. The exact influence of ULTRA is debated, but a typical assessment is that the Victory in Europe Day was hastened by two years because of the decryption of German ciphers.