Realistic water drag physic

To see the difference, just drop unit into water at some speed and see this difference:
Old behaviour: unit hit sea floor instantly.
New behaviour: unit slow down when hit water surface and gradually fall to sea floor.

Another difference is the reaction to sudden impulse. In ZK, fire atomic bomber (armcybr) on submarine (corsub), the difference is:
Old behaviour: submarine bounce off water.
New behaviour: submarine implode toward epicentre of explosion.