The M-209

The M-209 was a small mechanical cipher machine carried by US forces in World War II and Korea. Six wheels of different sizes carry movable pins, and a drum of 27 bars carries lugs. For each letter, the pins that are active and the lugs they touch decide how far the letter is shifted, and the wheels step so the shift keeps changing. Like Enigma, encoding and decoding are the same step.

The settings start as the example from the M-209 manual, which turns 26 A's into TNJUW AUQTK CZKNU TOTBC WARMI O. To decode a message, enter its six starting letters, the active pins on each wheel, and the 27 lug bars as two-digit pairs, where 0 means no lug.

Reading the output

The real machine printed a Z for each space, so decoded text looks like ATTACKZATZDAWN.