Talk:Experience and Rank/@comment-77.250.16.8-20141101184310/@comment-25477086-20141101184849

You can see in the combat section, but generally you need to either sink the flag for a B, or sink 4/6 ships for an A

You are getting a C because you inflict less than 3x the proportional damage to your opponent which tends to happen often, and aren't sinking enough of their ships or their flag.