Solid and well put Chris.
The very slow underwater sped of the U-boat worked against it when located , search equipment was much better than any tactics which might be employed to evadecapture of some U-Boats 570 in particular allowed 1st rate info to be gathered as to dive depth and construction of the submarines.
The tactics as employed by Walker et. al made escape difficult if not imposible location as Chris stated often ment death.
Opening distance to alow a fish to arm was often not posible and the time and numbers of escorts employed ..esp. later in the war made it a very chancy option acustic eels having been largelyanicipated and effectively countered.