Alright, have been trying to complete the Following In His Footsteps quest for quite a long time now. I eventually found my way to Chevy Chase, but i have not been able to get the battle to trigger. From what I've read the Brotherhood shows up and helps you defeat the super mutants but mine wont appear. I checked my quests and oddly the quest had been greyed out, indicating that it had been completed. But it hasnt! The quest check marks that i had discovered GNR (which i havent). GNR appears on my map but i cannot fast travel to the location because "i have not discovered it yet." So what the heck is going on? Thanks for the help
I don't know about getting the BoS to show up, but when you come out of the tunnels GNR is pretty close. If I remember right, head left (probably a couple of muties here), watch for the tunnel/hallway on your left just a short way down the street, follow it around. You should come up on a destroyed building with some more super mutants hanging out in it. Head up top and shoot the two or three that are up there, and then its pretty easy to pick off the others through the holes in the floor. Drop out of the building from the second floor right into GNR Plaza.
If you've completed or even started any of later quests in the main questline this one is automatically greyed out. The brotherhood won't show up and you'll have to kill the behemoth without the Fat Man. Sorry mate. Sheepbiter 10:12, March 18, 2010 (UTC)
This happened to me as well. I managed to kill the behemoth with a hunting rifle, laser rifle and many head shots. Three Dog's quest was still available but the reward was the location of a stache of weapons.