For 'gain the advantage', You have it for the round it succeeds and the next one, unless the other ship performs 'gain the advantage' at one difficulty higher. If they get advantage, it cancels yours for that round and they have advantage until the end of the next round, unless you take it back, at another difficulty higher. In practice, after a couple back and forth, both ships end up doing an 'Evasive maneuvers' to break off the sequence and then re-engage.