Underwater things seems to be an ignored concept on iEra. I think a loooong while back something was suggested a while back like this but... Anyway, maybe there could be an underwater gmap, peppered with secrets. As for combat, just remove the flippers and boost everyone's underwater swimming speed and give em all a free Russian APS underwater assault rifle. Just a very random sugestion, but still, underwater hasn't really gotten enough attention.  

Sounds cool  

And some levels underwater where its a normal room,like an underwater base or spar  

I like this idea.