I bought the Silent Hunter series from Steam a little over a year ago, SHIII, 4, and 5. The problem isn't your computer, its the Steam version of the game. I also had many issues of the sort you are dealing with, and saw a similar large gathering of destroyers while trying to do a photo recon op in Tokyo Bay. It seems the Steam version is actually unpatched and unpatchable. I'm not sure what version they offer for download, but I had whatever that is, with the U-boat missions as well, and had repeated problems with the game crashing and not wanting to run. I downloaded the 1.4 patch for the retail version of that game, but that wouldn't work because the installer couln't find the program on my machine, even though I pointed it to the proper folder. When I contacted Steam "support" about this they told me the game automatically updates itself... yeah right.
I uninstalled the Steam version and bought another copy of the game from Amazon.com. I never had such problems again. For the most part the game is very stable, even with mods activated, but whatever you decide to do, I would advise that anytime you save a game and quit back to the main menu, close the game down and then reload it before trying to play a single mission or war patrol scenario. Its been my experience that quitting out of one part of the game (career for example) and then loading another mode of gameplay (single mission, etc.) ends up corrupting the saved game files. Other people have had their own issues with loading saved games, and their solution is to never over-write a saved-game file. I don't need to do this myself, others do. At any rate, sorry about wasting your money on the Steam version. My experiences with Steam over the last few years forced me to conclude that they are no longer worthy of my dollars.
