Kill 25 Helghast soldiers with the VnD-10M Siren

During the chapter, Hidden Pasts, you will enter a Helghast Missile Base through a broken wall. After you do so, you will get ambushed by enemy soldiers and APCs. There are two Sirens located along your path, but you may as well only use the first one you come across.

Like the Scylla, this weapon has a cooldown system installed, but not as strict. Tap instead of holding the fire button to prevent overheating. After you kill all the enemies, restart from the last checkpoint, and do it all over again until you earn the trophy.