To complete the quest, the Vault Dweller needs to head northwest of the bunker on the world map. After a few days of travel, the military base will show up. Entering the location is considered scouting.
When the existence of the base is revealed to High Elder Maxson, he convenes with the remaining Elders and the Vault Dweller may attempt to convince the Elders that he requires Brotherhood assistance in storming base or Cathedral.
Once Maxson gives the quest, the player needs to ask for an additional weapon. He will then redirect them to Mathia, who will allow the Vault Dweller one of the following: