Why was Hall concerned that the Germans would learn about the British reading their secret messages?

Hall was concerned that the Germans would become aware of British capabilities to read their secret messages, which could compromise intelligence operations and lead to the loss of a strategic advantage. If the Germans suspected that their communications were intercepted, they might change their codes or adopt new methods of communication, rendering British intelligence efforts ineffective. Additionally, such awareness could heighten tensions and alter the dynamics of military planning and decision-making. Overall, Hall's apprehension centered on the potential operational setbacks that could arise from exposure.