The M-209 is an entirely mechanical rotor-based cipher machine, about the size of a small lunchbox, and designed by Boris Hagelin.
It was
similar to his C-38 cipher, but the design was simplified and made more rugged to withstand battlefield conditions. Production
began in 1942 and by the end of WW2 over 140,000
were made at a cost of $64.00 each. The Navy version of this cipher was called the CSP-1500. It was popular for its
light weight, small size and ease of use. It was never considered a secure cipher, so it was used for tactical,
battlefield messages where the intent was only to delay the enemy in reading the message by a few hours.
The M-94 cipher wheel was still in use until this new cipher machine was widely adopted in 1943. The M-209 was manufactured
by Smith & Corona Typewriter Co. under license from Hagelin's firm. This transaction made Hagelin a millionaire (when that
term meant something) and perhaps the only person to strike it rich from cryptology. The M-209 was still actively
used through the Korean War and until the mid-1960s.
The M-209 has a fixed rotor design with a "pin and lug" mechanism to provide an irregular stepping of the rotors. The
6 fixed rotors have a mutually prime number of settings (26, 25, 23, 21, 19, 17), giving a maximum message
length before repeating the cipher of over 101 million. Behind the rotors is a large drum which is used to set the
points which would step each of the rotors, allowing for highly irregular stepping. Twisting a lever switched between
"C" cipher mode or "D" decipher mode. The letter Z was reserved to print out a space in decipher mode.
Pictures of My Cipher Collection
Pictured above are the Hagelin M-209-A and M-209-B cipher machines and other US WW2 field equipment used to send
ciphered messages to and from the battlefield. The field phones were for voice calls and were only as secure
(or unsecure) as the phone line.
