Hi,
just to throw in some info from reread book chapters, the trick of the U-boats in the early war was to go in surfaced at night like a "Schnellboot", shoot from less than 400 meters if possible, and just keep up speed and reload. Diving was only done in almost hopeless conditions.
This is why escorts had a hard time, their ASDIC was useless against surfaced targets. Radar did not work under 1000-1500 meters, and not above 8000 meters. As well most escorts simply did not have radar until 1942. There is certainly propaganda still active today.
And there are numerous witness reports of U-boat crews that escort ships were passed at less than 300 meters, and they did not even see the U-boat. Even when they did see it and both had different courses they would pass each other so quickly that the U-boat did not need to dive, because the escort would lose the sub anyway in the next seconds - but try this in GWX and you'll be dead already in 1939
Greetings,
Catfish