One passage from the U-boat Commander's handbook:
When to Transmit Messages .
70.) Messages for the transmission of which no special time has been fixed should be transmitted, as far as possible, in the evening or during the night, and before important changes of position, in order to frustrate a possible reaction of the enemy to a bearing by sending into action antisubmarine formations or aircraft, or by diverting ships or convoys.
It's just great to watch SH3 develop! one by one the chapters come alive as the modders better the game