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US Army M-209 Cipher

M-209 in the Field
M-209 in action during WW2

The M-209 is an entirely mechanical, rotor-based cipher machine designed by Boris Hagelin. It is about the size of a small lunchbox. While the design of this cipher machine uses rotors, they are not the electro-mechanical type used for scrambling the alphabet, as is the case in the Enigma, Hebern or earlier Hagelin devices. Instead, the M-209 was designed so that the rotors mechanically activated a pin and lug mechanism which was used to select a reciprocal alphabet. This represents a completely different cryptological technology, which is also used by the the Transvertex HC-9.

The 6 fixed rotors of the M-209 have a mutually prime number of settings (26, 25, 23, 21, 19, 17), giving a maximum message length of 101,405,850 characters before repeating the cipher. Behind the rotors is a large drum which is used to set the pins and lugs, which then selects the enciphered or deciphered character. Twisting a lever switches between "C" for cipher mode or "D" for decipher mode. The letter Z was reserved to print out a space in decipher mode.

The M-209 was similar to the Hagelin 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. 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-94 cipher wheel was still in use until this new cipher machine was widely adopted in 1943.

The M-209 was still actively used through the Korean War and until the mid-1960s. 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.


M-209 Ciphers
US M-209A and M-209B cipher machines.


Pictured above are the Hagelin designed US M-209A and M-209B cipher machines which were used in WW2 by the US to send ciphered messages to and from the battlefield.

The M-209A cipher machine is on the left and was made in 1942 in Philadelphia. It is serial number 214, making it one of the earliest of the 140,000 manufactured during WW2. There are Signal Corps stamps inside the inner lid and on the bottom of the machine. Inside the lid is the decal "Manufactured By L C Smith & Corona Typewriters Inc." The paper tape roll is in the lid. Missing are the tools normally in the lid, one of the 4 rubber feet and the letter counter.

The M209B on the right was made in 1944 in Philadelphia and is serial number 54921. The "CACH" following the serial number is the manufacturer's code, which stands for the Smith - Corona Typewriter Co. It is clearly stamped with the orange Signal Corps markings with "SC 987" inside a triangle and a date stamped in red ink of Jun 16 194?. Barely visible is a previous marking of "C-213" then painted in large block lettering is: "HQ & HQ 47th Comm Sect." There are two more Signal Corps stamps, one on the bottom and the other inside the inner lid. The paper tape roll is in the lid as is a pair of tweezers and an aluminum tube holding spare ink rollers, which is stamped "I" on the top. The slotted tip screwdriver and tube for oil is missing.

After first receiving this cipher, I moistened the ink roller with a couple drops of water and you can see the printout on the paper tape. It looks like it is as ready for action as it was over 60 years ago.

The differences between the two models are only cosmetic.


Copyright © 2016 by Ralph Simpson - Creative Commons Attribution-ShareAlike 4.0 International License