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ECM Mark II codename SIGABA
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The ECM Mark II was a cipher machine based on the electromechanical
rotor principle. It was developed by the USA shortly before WWII and
has been in service until the 1950s.
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The machine is better known by its codename SIGABA.
The official Army designator for the machine is Converter M-134,
whilst the Navy called it the CSP-888/889. A modified Navy version
is known as the CSP-2900.
The drawing on the left was taken from
U.S. Patent 6,175,625
that was filed in 1944 but not issued until 2001.
As far as we know, SIGABA was never broken.
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SIGABA had three bank of 5 wheels each, the contacts of which
are visible in the drawing above. The main bank (at the rear)
contained 5 wheels with 26 contacts each. These were the main
cipher wheels and worked similar to
the Enigma machine.
The second bank (middle) also contained 5 wheels with 26 contacts
each, but these were used to control the movement of the main
cipher rotors. These were called the control wheels.
The third bank (front) contained 5 wheels that were smaller
than the others. They only had 10 contacts each and would not
move during encipherment. Together with the control wheels,
controlled the movement of the cipher wheels.
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Combined Cipher Macine (CCM)
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SIGABA was also adapted for interoperability with a modified British
Typex machine. The common machine was known as the
Combined Cipher Machine (CCM), and was used from November 1943.
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It was used for secure Allied communication during WWII and even
served with the newly established NATO for a few years after the war.
The wheel assembly was removed and replaced by an assembly of just
5 coding wheels. Less secure than the original, but interoperable
with a modified British Typex.
The machine shown here is one of the very few CCM versions of
SIGABA that have survived. Unfortunately, the wheel assembly is
missing from this one.
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Furthermore, the motor-assembly has been removed, so we assume that
this machine has been used as a donor for spare parts in order to
repair other machines.
If you have any parts for this machine or if you have additional
information, please contact us.
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