Mission: Fission
Near the beginning of the mission, you're teammate will notify you of the Mobile Defense Turret. Quickly go up to it and enter it. It has two different fire modes, but for the achievement/trophy, you want to use the bumper to "mark" enemies, and then let go for the homing missiles to kill the enemies.
You can stay at the mobile turret spawn, and slowly keep waiting for more enemies, but I recommend going a little forward for lots of enemies (15+) to spawn along with tanks/choppers. Make sure you don't go too far forward, or the turret will break, and you will be kick out. You should have no problem getting 10+ kills with these homing missiles.