The Enigma machines were used during World War II by the Germans to protect their communications. It came in different models, but they all built on the same principles. It had a keyboard, rotors, a plugboard, a reflector and a lampboard to show the results. The Enigma machine encryption was broken during World War II by military intelligence, mainly through operator mistakes and Allied capture of key tables.
See also: Code-Breaking overview | Adfgvx cipher | Adfgx cipher | Affine cipher | Atbash cipher | Baconian cipher | Beaufort cipher | Bifid cipher | Caesar cipher | Columnar transposition | Cryptogram | Double transposition | Four-square cipher | Gronsfeld cipher | Keyed caesar cipher | One-time pad | Pigpen cipher | Playfair cipher | Rail fence cipher | Rot13 | Trifid cipher | Variant beaufort cipher | Vigenere cipher