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M-209 Cipher Machine
The M-209 Cipher Machine, designated CSP-1500 by the US Navy, is a portable, mechanical cipher machine used by the US military primarily in World War II, though it remained in active use through the Korean War.
It was designed by Swedish cryptographer Boris Hagelin and manufactured by Smith & Corona in Syracuse (New York, USA).
The M-209 was based on the C-38, which itself was an improvement of an earlier machine, the C-36.
The cryptographic strength of the machine was reasonable for its time, but was not perfect. As of early 1943, it was assumed that German codebreakers were able to break an M-209 message in less than 4 hours. Nevertheless, it was considered sufficiently secure for tactical messages which, due to their nature, would be meaningless after several hours.
The M-209 was a rotor machine similar to a telecipher machine, such as the Lorenz cipher and the Geheimfernschreiber.
It was about the size of a small lunchbox and weighed 6 pounds (2.7 kg).
The machine was used for enciphering and deciphering messages in the field and was small, light, rugged and dependable and required no batteries.
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.
The M-209 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.