For me it was Silent Service on the C64, then Silent Service 2 on the Amiga. I really got into years later with Jane's 688i though. That was the best sub sim around at the time, which led me onto SH2, then 3,4 & 5! I still have 4 & 5 and I also have Sub Command and DW.
Silent Service 1&2 are now available on GOG.com for a small fee.
