modern day? what do you mean, recently produced? or like subs they use today? if you are thinkign new subs, there was a good sim, similar to silent hunter, but it was with new US and other superpowers subs, if i can find the name i will be happy to share it with you, tanks on the other hand...i cant help you there
Janes combat simulations has a good one called 688(I) hunter/killer, i have not played it, but i have heard it is pretty good, it is a sequel to the origional "sub command"
Jane's Combat Simulations - 688(I) Hunter/Killer I simply googled Modern Sub Game and thats what came up. Wouldnt be able to tell you how good it was etc, but googling it should bringup some reviews too.
To my knowledge, it's the really only one out there. I've played it a couple of times (years ago) I didn't really like it. SH series is a lot better!