A four-rotor Enigma cypher machine with a second operator display ('remote lampboard') (S/n 765). This is a variant of the Enigma K cipher machine developed in Germany in 1927. This type of machine, known as a Swiss-K, was supplied to the Swiss government in 1939-40 for use by the Swiss Army and Air Force. Although having four rotors, the fourth is the reflector, so it is not a true four-rotor machine.