M-209 Home Page
M-209 Workings Home Page
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Prepare the machineBefore cipher (or decipher) a text, we must prepare the machine by setting the key in accordance of our cipher organization. The key is divided in two parts:
For the internal key, we use the example present in TM 11-380 manual of 1944. We set the external key to "PEOPLE" The basic principle, the role of typewheel during ciphering (or deciphering)In M-209, the most important part is the typewheel which have three alphabets. Here are the three alphabets (from left to right):
The code clerk chooses a letter (a plain letter or a ciphered letter) on the indicator disk, I.E, he turns the typewheel to put the letter in front of the bench mark. Then he actions the drive knob, the typewheel turns (in counter clock wise) of several letters. The code clerk can see the result (the ciphered letter or the plain letter) on the reproducing disk. At the same time, the printer mecanism printed the result too by means of the typewheel disk.
Remark:
The internal mechanism (Drum bars and Wheel pins)We have just seen that the typewheel turns. But why is it moving?The operator turns the driveknob. Each of the 27 drum bars passes front of the guide arms. If at least one of the two lugs of a bar is in effective position front of a guide arm which is pushed forward, so the bar that carries the lug is shifted to the left and turns the Typewheel of one letter (in clockwise) by means of intermediary gear. Then, during the motion, the typewheel turns from zero to 27 letters depending on which guide arm is forward and how many lugs are in effective positions front of them.
When driveknob ends his turn, several operations take place:
References
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