Hope you guys are doing as well as can be under the circumstances. Back on the subject of attacks, I usually find that I am never kept down too long so that repeated attacks are impossible - once the DD's leave me alone I almost always use the "end run" method, racing parallel on the horizon, so I can set up another attack the following night. Unless I am low on torpedoes, damaged, approaching shallow water, or have orders to patrol elsewhere. I'm pretty sure that historically, Donitz would regard just one attack on a convoy as not being enough - leaving you in trouble once you got back to base.
And I agree night vision by non-player units is too good in stock; but I usually do OK by going to PD & using the periscope only occasionally when I get closer than maybe 5000M.