Welcome to Subsim, Bama
There are a great many supermods out there. GWX 3.0 gold seems to be the gold standard if you will excuse the pun with regards to Silent Hunter 3.There is also the war elite mod and NYGM mod.
Subsim Member Rockin Robbins was working on Fall Of The Rising Sun FOTRS for Silent Hunter 4.
Subsim Member " TheBerbster " was doing some work with the " Wolves of Steel " Supermod for Silent Hunter 5 and tells me the bugs have been worked out of it and the game play is excellent.
All of these mods should enhance the gameplay of your respective simulations. With regards to Steam, a number of our members have reported problems with Silent Hunter games from Steam. If you can find a Silent Hunter DVD, get it.
Enjoy your time here and your Sims and welcome aboard.