My very first Sub Sim was Silent Hunter on the Commodore 64. That and F-15 Strike Eagle where the very two first games I played on it.
The coolest thing was my fathers uncle was over watching me play it (I was about 11-12 at the time) and they had a copy protection scheme where you had to look up the class of destroyer in the manual to play. Well my Fathers Uncle was in the USN during WW2 and he was able to tell me what they where before looking them up in the manual!