Reply #18: Perhaps the lights also helped

[Mendocino]

with navigation. Simply put, before the advent of GPS and other systems like LORAN, submarines and other vessels still had to navigate using sextants. A sub would have to surface every so often to take sun or star shots. The bright lights of a New York or Boston would simplify this process. Head for the lights and wait in the near shore waters for a target to appear.

Also in regards to #8 and #11, yes U-boats did prefer to to surface and use their deck guns. A few shots with cheap and easily carried shells would sink most merchant ships. A small cramped U-Boat could carry many shells relative in proportion to the space taken up by torpedoes and their tubes. Torpedoes would be used more for large targets and armed ships.