This Enigma Key-List was provided for a 3-Rotor Heeres/Luftwaffe (German Army and Air-Force) Enigma cypher machine. As these sheets provided the key to the Enigma cipher for an entire month there were some security features: Air-Force sheets were not to be taken on board planes, Naval sheets were written in soluble ink and as key-sheets were written bottom to top, the current day’s key was cut-off the sheet every day.