I started off playing Destroyer Command, but after I found Blind Man's Bluff in a closet in our house (along with The Hunt for Red October and a bunch of other Tom Clancy books), I decided I wanted to play from the other side of the sonar screen, so I bought SHIV. When I discovered my computer couldn't handle IV, I found SHIII, and decided I liked subs more than destroyers

Still don't have a decent enough machine to run SHIV, but soon...
I've also always been fascinated by subs (well machines of any kind, but subs are a lot cooler than most), especially early ones, and my grandfather was a submariner, so maybe it runs in the family