Recently new information was published on the M-209 cipher machine and this information coupled with all the material that I have collected over the years led me to write a new essay on the M-209 cipher machine and its exploitation by the German and Japanese codebreakers.
The new
essay is:
At the start of WWII, the US armed forces used various means for enciphering their confidential traffic. At the lowest level were hand ciphers. Above that were the M-94 and M-138 strip ciphers and at the top level a small number of highly advanced SIGABA cipher machines.
The Americans used the strip ciphers extensively however
these were not only vulnerable to cryptanalysis but also difficult to use. Obviously a more modern and efficient means
of enciphering was needed.
At that time Swedish inventor Boris Hagelin
was trying to sell his cipher machines to foreign governments. He had already
sold versions of his C-36, C-38 and B-211 cipher machines to European
countries. He had also visited the United States in 1937 and 1939 in order to
promote his C-36 machine and the electric C-38 with a keyboard called BC-38 but
he was not successful (1). The Hagelin C-36
had 5 pin-wheels and the lugs on the drum were fixed in place. Hagelin modified
the device by adding another pin-wheel and making the lugs moveable. This new
machine was called Hagelin C-38 and it was much more secure compared to its
predecessor.
In 1940 he brought to the US two copies of the hand
operated C-38 and the Americans ordered 50 machines for evaluation. Once the
devices were delivered, they underwent testing by the cryptologists of the
Army’s Signal Intelligence Service and after approval it was adopted by the US
armed forces for their midlevel traffic. Overall, more than 140.000 M-209’s
were built for the US forces by the L.C. Smith and Corona Typewriters Company.
(2)
The American version of the Hagelin C-38 was called Converter M-209 by the Army and USAAF and CSP-1500 by the Navy. Compared to the original version it had a few modifications. The M-209 had 27 bars on the drum while the C-38 had 29. Another difference was that the letter slide was fixed. During operation the text was printed by setting the letter spindle on the left to the desired letter and then turning the hand crank on the right.
The M-209 was a medium-level
crypto system used at Division level down to and including battalions
(Division-Regiment-Battalion) (3) and even up to Corps for certain traffic. The
USAAF used it for operational and administrative traffic and the Navy aboard
ships. SIGABA was used for
higher level messages (Army-Corps-Division) and hand systems like Slidex and the
Division Field Code used for tactical messages (Battalion-Company-Platoon).
The Germans called it ‘AM
1’ (Amerikanische Maschine 1)
and the Japanese ‘Z code‘.