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It is worth noticing that the numerals 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 are associated with the keys of the top row of the typewriter keyboard, taken in order from Q (on the left) to P (on the right).
The conventional names 3 4 5 8 9 / have no connection with the meaning of ordinary occurrence of numerals and punctuation on the typewriter keyboard in figure shift, but are just names given to those keys and electrical signals which do not correspond to any of the 26 letters of the ordinary alphabet. For example the transmission by teleprinter of the phrase 'PRICE 3/6' would involve the following electrical signals being sent in order 9PRICE95EXY89. Similarly a full stop is sent as 5M89 and a comma as 5N89.
A teleprinter message can be thought of as a stream of "Letters" corresponding to the keys depressed and the electrical signals sent during transmission.
(b) Five-impulse Tape.
For speed and accuracy in transmission, long teleprinter messages can be 'perforated' in advance and transmitted automatically from five-impulse tape (AUTO) instead of by hand operation of the keyboard (HAND). The tape from which the transmission takes place is made of paper and gives the sequence of signals to be sent, each signal being represented vertically as a set of five impulses with a blank for every dot and a hole for every cross. The tape for 'PRICE 3/6' would look like this
|Sprocket holes (used to drive tape)||.||.||.||.||.||.||.||.||.||.||.||.||.||.|
Similarly the receiving teleprinter can be made to punch a tape, instead of, or in addition to, printing the message when it arrives.
(c) The German Ciphered Teleprinter.
During the war in Europe in 1940-5 the Signals Units (FUNKTRUPPEN) attached to German service authorities were issued with a novel type of WT and cipher equipment for communication with Berlin and other Headquarters stations. Receiving and sending teleprinter equipment were used but the electrical signals corresponding to the various teleprinter letters were not normally transmitted from sender to receiver by cable but sent out over the air in ciphered form. Cipher machines (SZ or SCHLUESSELZUSATZGERAET) were therefore interposed between the sending teleprinter, which converted the message into a sequence of enciphered impulse-signals, and the transmitter which sent the ciphered sequence over the air, and similarly between the WT receiver and receiving teleprinter.
These cipher machines were given (by us) the general cover name of FISH and two particular features should be noticed
(i) the cipher was not directly applied to the message, which was reduced to teleprinter form before being enciphered
(ii) the cipher text was never seen by sending or receiving operator, as no recording device was interposed between cipher machine and WT transmitter or receiver.
(iii) the receiving teleprinter printed on to continuous sticky tape, so that not only / but also 3 (carriage return) and 4 (line feed) did not occur in the unciphered stream. There was no bell.
The equipment of a mobile FISH signal unit was housed in two trucks:
(a) The BETRIEBSWAGEN carried two cipher machines (for sending and for receiving) and teleprinter equipment for sending either from keyboard or from tape, and for receiving and printing. In addition, it carried a device for perforating five-impulse tape from a message by tapping it out on a keyboard.
(b) The SENDUNGSWAGEN carried the WT transmitter.