I watch a show about WWII submarines. After Pearl Harbor they send 4-5 submarines of a new class with large dimension so can have bigger autonomy range. This was related to the first German waves to the USA East Coast and the great success of one Nazi captain because american didn't have enough resources to defend their coast.
But there are some incidents make me wonder what happen.
1) During day the submarine stay on the sea bed and go hunting during night. But on one opportunity the submarine went up too early and still was some daylight and one American plane detect it and throw some explosives.
Why the submarine go all the way up? Why don't go to periscope level first to take a peek? That would be enough to realize there is still daylight and even if were already dark watch for any close threat.
2) After sunk a ship instead of killing the survivor the submarine just go away. I have seen other episodes where the submarine crew use machine guns to kill all floating survivor. Is that a tactic implemented later? On this case the survivor went and alert about the submarine presence.
3) With very low number of torpedo remaining, the submarine decide to use the boat deck gun against one small cargo vessel but when the gun didn't work right away they went for the torpedo.
Why they didn't continue shooting with the boat deck gun? My guess is if the submarine has that weapon is for something, but if can't handle a defenseless boat why they put it there.
4) At the end without any torpedoes and low fuel they were returning home but were spotted by a whaler transformed into oil tanker, the whaler was going in a collision curse and because the submarine has engine problem was going 1 knots slower than the whaler. Finally they fix the engine and could escape by going 0.5 knots faster than the whaler.
But why they don't use the deck gun to scare the whaler?