Modern day subsims are sensor battles,which can be quite interesting if you love it...but you have to place them in a 'WorldWar3' scenario to make it interesting..
The thing i really love about for instance Red Storm Rising is stalking the big boomers,trying to attack them and sink them before its escort arrives.It can be quite a challenge..
Some other things come up to mind...you wont see the sun for a couple of months and call me romantic but sailing my boat into a beautifull sunset while listening to some sweet tunes by the Andrews Sisters can be quite relaxing...yeah i know
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Like i said before just make a subsim with a timeline so we can sail what we want!