[Gustav Schiebert]

IRL U-boat commanders had much the same problem. That's why neutrals usually light up their flags like the 20th Century Fox sign - and why regulations usually referred to areas in which 'unlit merchants', rather than 'enemy merchants', could be sunk. Generally the zones were widely known, so neutrals in the area had no excuse if they were sunk. I seem to remember you get radio messages telling you the unlit sinking zones throughout the war, but this isn't reflected in the renown system.

In reality, if you sunk an unlit merchant at night in the North Atlantic you wouldn't be penalised.