I have Aces of the Deep but never installed it
I played a more recent and excellent U-Boot sim called
Silent Hunter II (by SSI).
It's quite thorough but still easy to play. You can try all U-Boot types, even Type XXI.
Last week, I played after reading "Das Boot" and I was depth-charged for 2 hours, exactly like in the movie. I was getting good at judging when to evade based on the sound of the destroyers.
SSI also makes a companion destroyer sim called
Destroyer Command. You're in command of a single destroyer, or a group of them.
Both games can be played on the Internet, and of course you can play sub against destroyer.
Here's the
manual (pdf, 2 megs)