At the beginning of the 20th century, secure communication channels were a pressing need for the military. In World War I, armies mainly used code books and simple substitution or transposition methods to encrypt secret messages. These methods usually involved replacing letters in the plaintext with other characters or letter combinations.

Over time, skills in the field of cryptanalysis advanced: increasingly complex methods were employed, yet human-to-human error remained high. The technological development was not advanced enough for broad machine use.

The weaknesses of those early methods later led to the desire for powerful, automated cipher machines such as the Enigma.