Okay, then. Grenades would probably sink faster. I could see using the chaingun and the rocket launcher underwater, and the other weapons just shut down or something. Also, I think there should be an oxygen meter just to keep people from camping underwater for ambushes that may or may not happen. Yes there is fancy technology that the legionnaires have, but gameplay has to be considered as well. PUBs, while this could be fun, would turn into an underwater tea party with rockets. However, there are tactical advantages to being able to sink your opponents. For example, as a chaser, you can sink the capper, or, as somebody else pointed out, a capper could, with a well-placed shot, sink a chaser and buy some valuable time to get away.