I'm pretty sure that we'll indeed see a Pacific War subsim quite soon.
Since SHIII is selling extremely well for a sim I'm sure UBISoft got the hint. IIRC there actually has already been an announcement for a successor.
With the grafics engine, AI, weather engine etc. already in place it shouldn't take them too long to produce a Pacific War game.
I just hope there will be also british and dutch subs besides USN ones. And maybe even *gasp* japanese ones...
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"...late afternoon the Air Tasking Order came in [and] we found the A-10 part and we said, "We are going where!? We are doing what!?"
Capt. Todd Sheehy, Hog pilot, on receiving orders during Operation Desert Storm