This is for completing the side mission on "Anathema unto god". You will get to a point where there will be a cutscene with a girl standing on top of an enemy called "A hellfire" dont follow the mission objective here, make a right, pick up the mininuke at the objective marker and then clear the area. To make this easier make sure you have infinite ammo turned on and even tourism difficulty or play on co-op and set respawn timer to 0.