in player vs. player battles the winner should be awarded battle points when they defeat the loser(who still loses their EP and possibly helix) these points vary by level and sub type that the loser has. As one earns these battle points, they can move up ranks. the rank your at will be displayed on your submarine next to your HP/SP meter as a symbol. ex: seaman 1 = a bronze diamond shape. more points means you unlock some items at the merchants shop. If one obtains enough points, the Skonos can be purchased.
Pvp battles wont award points if you sink the following subs:
the Scion Jafhnar counter-parts the reason is likely becuse thare cadet subs
your first kill will get you 10 points all others discounting cadet subs get you 1 bp