One year into the war, 400k tons sunk, all thanks to the T2 with impact detonator set to minimum depth. Fire range 500-1000 m for single targets, 3000-4500 for heavily guarded convoys. A magnetic detonator should break any ship in half but while using them I actually had worse results even when they did explode on target. Even 2 popcicles coouldn't bring down a medium cargo. Maybe the damage model isn't that good and can't count in the flooding effects?
