The game rules regarding submarines not making a sea zone hostile do not seem to reflect the realities of what submarines did in WW II. The Allies developed anti-submarine forces and the convoy system to fight the German submarine threat in the Atlantic theater and were, after a time, able to virtually eliminate the submarine threat from this “hostile sea zone”. On the other hand, the Japanese never bothered with anti-submarine forces or the convoy system and, by the end of the war, Allied submarines had essentially run out of targets to sink.