Definetely more interior views with full roaming capability of all compartments. Era correct radio broadcasts/music, Tokyo Rose and more radio traffic. Enemy submarines to duel with, more coordinated attacks against the enemy using suface ship,other subs and aircraft. Warning when in time compression that an enemy is approaching so you don't have a destroyer coming out of nowhere with guns blazing while you are t/c'ing your way through quiet sectors getting to your patrol areas.
