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During WWII, the Swiss Army was using a modified version of the
commercial Enigma K machine, which is
sometimes referred to as the Swiss K.
After the Swiss discovered that their Enigma K traffic was being read
by both the Allied forces and the Germans, they started the
development of their own machine, which they called NEMA,
the abbreviation of NEue MAchine (New machine).
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The machine is also designated T-D, which stands for
Tasten-Drücker Maschine (key-press machine). This is still
reflected in the serial number, which takes the form TD-xxx.
The official name is NEMA Modell 45.
At first glance, the machine appears to have 10 wheels, but
only 5 of them are electrically wired. Four of them are the
coding wheels, with 26 contacts at either side, just like
on the Enigma.
The 5th wheel (at the left) is the reflector which is moved during
encipherment, unlike the reflector of the Enigma K, which
can be set,
but does not move.
The other 5 wheels are the drive-wheels. They are mounted
on an axle in pairs with the 5 coding wheels.
A drive wheel has several mechanical cams that control the
turnover of the coding wheel.
The machine contains several improvements over the Enigma design.
It features, for example, irregular stepping, caused by
the addition of the drive-wheels, which makes the machine
far less predictable than an Enigma K.
But it has also inherited some of the weaknesses of the Enigma,
such as the fact that a letter can never be enciphered into
itself. The latter is a result of the use of a reflector
(or Umkehrwalze, UKW).
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The machine was developed between 1941 and 1943 by a team led
by Captain Arthur Alder (a professor of Mathematics at the
Bern University) and the first prototype was ready in early 1944.
After a few modifications and improvements, the machine was
finally approved in March 1945.
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The NEMA didn't become available before the end of WWII.
After the machine was approved in March 1945, it took quite
a long time before it became available, as the first machines
entered service in 1947.
In total, 640 machines were built by the Swiss manufacturer
Zellweger AG. Three different variants were in circulation,
which can be descriminated by their serial numbers:
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- TD-100 to TD-199, Foreign office
- TD-200 to TD-419, Training Machines
- TD-420 tp TD-740, Operational Machines
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The wiring of the machines used by the Foreign Office (FO)
has been kept secret. As far as we know, these machines have
never been released.
The training machines were used by the Swiss Army between
1947 and 1975. After that, there were only kept for emergency
purposes.
The Operational Machines, sometimes referred to as
K-Mob-Maschinen, were always kept under wraps. They were only
to be handed out in case of war.
Operational machines differ from training machines, in that they
have 2 additional wheels (stored inside the top lid) and have
different notches on the rings of their wheels. Furthermore,
they carry a label on the top lid, that says:
Nur bei Kriegsmobilmachung abgeben!.
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The NEMA was officially declassified on 9 July 1992.
A few years later, on 4 May 1994, the training machines and
the operational machines were offered for sale
to the public.
As far as we know, the FO machines were never released.
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- Geoff Sullivan and Frode Weierud, The Swiss Nema Cipher Machine
Cryptologia, October 1999, Volume XXIII, Number 4.
- Walter Schmid, Die Chiffriermaschine Nema
Self-published book with CD.
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