Well, depends on the definition of what constitutes really playing a subsim!
Me and my dad played Silent Service II on the Atari all the time, back when I was 12.
On the other hand... I was 12, didn't really know English - and my dad wasn't a sub expert by any means :p
But I have such fond memories of it that two years ago, in the pre-release hype of SHIII (just like we have for SHIV here now

), those memories flooded back and made me run out and get SHIII. In the years between I became a real flight sim fanatic, and yearned for a historical game with a good career mode. So, good memories + good campaign = CCIP goes to sea on a U-boat. Have been a subsim diehard ever since