Section 8: Prejudice

I actually did this trophy in the campaign, in level 6 where your objective is to repair the two turrets is the perfect spot. The area has been trenched out and the two turrets are at opposite ends. Enemies never stop spawning here, and they group together often on top of the ground outside of the trenches. Call a couple of napalm mortar strikes on the enemies until they die and the trophy is yours.