Scoop up Dangerous Waters, and the LWAMI mod for it from
www.Subguru.com
Then grab the Naval Combat Pack and get SCX/SCU for Sub Command from Subguru. And also grab the Fleet Command Naval Warfare Project addon from
http://forums.navalwarfare.org/showthread.php?t=66
You'll have your sub fix in no time !!! Look up the games here in the subsim store to purchase.