Re: Cribs from touch
This was part of Gordon Welchman's work that revolutionised military signals intelligence: Previously, everyone concentrated on the message content, but Welchman is credited with being the first to realise that what is said in a message is only part of the information that can be extracted from it. The identity of the sender and recipient impart information, as does the schedule of transmissions, the transmission power, and the attitude of the sender: a good Morse listener can't just recognise a "fist", they can also hear how relaxed or stressed that sender is, just a you can tell how relaxed someone is by their voice.
So, if you recognise an operator in Hamburg's keying style and know he sends lazily-keyed confirmations to messages about fuel supplies every morning, usually to other operators in the Baltic, but suddenly he's responding to stations in Dover and Rotterdam as well and with more urgency than his usual lazy fist, then it suggests that there's something happening along the Channel that might be worth sending a spy-plane to look at. And you discovered this without having to decrypt a single message.