For me it's SH4 ... hunting the Pac theater from Dec 7th, 1941 to the end ..
early days finding a convoy with no escorts and just plain runnin outta deck gun ammo
..ya .. fish in a barrel

..then comes the Japanese air patrols, the lethal DD's and escorts ..and hunting the shallows of the Java Sea
where it's *dangerous* to be in a sub ..when you can't submerge

Timing is *everything* ..even night engagements in the Java Sea are lethal if you make a wrong move.
Then there's the Sea of Japan .. shades of Run Silent, Run Deep!
Can almost hear Clark Gable 'We're going for a Bow Shot!'
Ya baby!
-Frank aka GE