I have fallen in love with the "decks awash" mod and recently have put it to good use for getting in real close to a convoy. The downside is that once you hit something [GWX Gold] the merchantmen all start playing searchlights all over you. Still, it's a handy technique and I have used it to get closer to a convoy in daytime than I would normally brave. In order to see how it works, go to the external view of your sub and hit the ";" key. You'll see the sub sink deeper into the water, but you can still view from the bridge. However, from the readme file it only works in relatively calm water. Using it in a storm will cause your sub to dive and broach.

I remember one of my first patrols out I ran right into the middle of a convoy. Scared the hell out of me. My watch officer says "Ship spotted!" I come up to the bridge and a merchant is no more than 20 feet off my port side. I was trying to infiltrate Scapa Flow right after the Brits declared war and I ran right into one of the sunken ships they use as barriers. impossible to see anything at 0130 in the morning with heavy rains. makes for a nerve-wracking experience.