Cryptome distributes an interesting link:
Let’s have a look at the language game in use back in US in the 1944 era. In contrast to Friedman’s military cryptanalytical texts (focused on generic analysis of Vigenere squares) we see what we would expected all along lots of signals terminology!
One sees that the very notion of privacy – in this field – is tied up with speech (and the telephone as the means of conveying speech). It’s distinguished from the world of codes and ciphers – involved in the data world of telegraphy. We have to remember that A2D is only just about to be invented (in a viable form).
The most interesting feature for me was the characterization of TDM as a scrambling system (vs a multiplexing notion). We have to recall just how primitive was “privacy” in these days – thought of as denying “real-time” exploit of the eavesdropping.
Finally, we note just how critical was the (voice) spectragram – using classical phase-space ideas to build (literally) a picture of noise whose evolution towards the solution shows the analyst how to solve the puzzle of the scrambling elements used by the target system (today).
one sees the constraints are, unlike in telegraphy decoding, based on the nature of voicebox for each human language upon sound formation. In combination with the spectragram these constraints enable the (military) analyst to cut down the search space of puzzling elements.