I don't think there's much you can do to (without cheating), so if it's a darkened ship I would just take a risk if it's in waters that are not that much used by friendlies. In the Mediterranean or the North Sea this risk might be too heavy, but in the Western approaches in 1943, for example, the risk is very limited.
I once read about someone playing this game in a dark room, another one playing with a red bulb light and another one with a shirt covering him and the monitor to see better in the dark. I guess gamma correction was not enough for those guys
