I've bought SW, U-Boat Leader, and Silent War. All are solitaire sub games, table-top games. UB Leader lets you command a flotilla, five or six boats. The other two let you command all subs that sailed. Silent War is the Pacific and Steel Wolves is the Atlantic. Monster games.
If I play Steel Wolves as they indicate in the manual, it should take me about 10 years to resolve the whole war. Yikes!
I recently bought a whole mess of WW2 board games to reflect all the major battles and events. I may never look up again!