Message Book M-210 was, as far as I have been able to determine, the standard form for recording message traffic during World War 2. A great deal of rigorous procedure was necessary to reliably route message traffic, and part of that procedure involved composing messages on the standardized carbon-copy forms in Message Book 210 prior to submission to message centers for routing. The same forms were used by message centers when transcribing messages (for example, after encrypting them with Converter M-209), when receiving messages sent via radio, etc.
Message Book M-210 was, as far as I have been able to determine, the standard form for recording message traffic during World War 2. A great deal of rigorous procedure was necessary to reliably route message traffic, and part of that procedure involved composing messages on the standardized carbon-copy forms in Message Book 210 prior to submission to message centers for routing. The same forms were used by message centers when transcribing messages (for example, after encrypting them with Converter M-209), when receiving messages sent via radio, etc.