The stealth of the submarine creeping up ready to pounce on the weak pathetic enemy is what makes me want to play subsims. Attack then slip away to fight another day.
Plus i like submarines
Edit:
First game that got me hooked on subsims was Aces of the Deep - everyone here probably played it so will agree its a classic. Then i tried my skills in Fast Attack which was about modern subs but easy to play and a great game. Then i thought well im pretty good at this so tried Sub Command....

Boy that game sent me through the ringer without any mercy. The print out manual was a few inches thick, the learning curve was steep. Sub command is the navy sim of what the flightsim Falcon 4 was - Hard. IMO. I remeber trying a few mods like SCX which improved the gameplay and graphics. Dangerous Waters was another i tried. I long to learn this game but just haven't the time - WW2 sims are more easiler. Somewhere in there i played all the silent hunter series right up to the now SH4.