Tom Clancy's H.A.W.X.

This is probably the first weapon related trophy you will obtain as you play online. The reason for this is that the Joint Strike Missile is the most commonly used weapon, and is available with most of the planes. You don't really need to try too hard for this as the missiles lock on to their enemies. Once you are locked on to your desired target, shoot, and hope that he does not dodge it. Unless you come across some really skilled pilots who dodge everything or you're not all that good at the game, this will be a piece of cake. Once you get the required amount of kills, this trophy will be yours.