Incidentally: Karl Dönitz - Wikipedia
Dönitz was deeply involved in the daily operations of his boats, often contacting them up to seventy times a day with questions such as their position, fuel supply and other “minutiae”.
This incessant questioning hastened the compromise of his ciphers by giving the Allies more messages to work with. Furthermore, replies from the boats enabled the Allies to use direction finding (HF/DF, called “Huff-Duff”) to locate a U-boat using its radio, track it and attack it (often with aircraft able to sink it with impunity).
