[CB..]

if it's early in the campaign and the merchants haven't got deck guns yet then i reckon the only safe tactic in the very thick fog is to attack with the deck gun (if it's calm anyway) other than that give them a wide berth during poor visability ;as you say by the time you've got them within visual range theyre too close for torpedos-- and they just love to ram you

i avoid them like the plague in thick fog