The Best Defense

The Best Defense is a main quest It is the final quest in first act of the Brotherhood questline.

Background
Paladin Rahmani's actions have cut the Brotherhood First Expeditionary Force from Lost Hills permanently and Knight Shin is on the verge of mutiny. However, a more pressing matter has appeared: Fort Atlas comes under attack!

Walkthrough
The quest is the culmination of the Steel Dawn quest line. Upon arriving inside Fort Atlas, Scribe Valdez is busy reporting to Shin and Rahmani about the situation: Super mutants have blown a hole through the substructure and are pouring into the facility, with the initiates holding the line as best they can. Upon talking to her (and venting frustrations about being the only initiate to pull their weight, which has the rare distinction of making Rahmani, Valdez, and Shin take offence), the next goal is to bolster the barricade in the substructure.

Down below, the barricade and the initiates are holding the line in between mutant attacks. Valdez will explain that the attacks have been occurring in waves for several hours, and the situation is a war of attrition they cannot afford. Rahmani will propose taking the fight to the enemy, to which Shin reacts poorly, considering it a suicide mission. However, when Valdez explains that she has explosive charges prepared as a last resort, which can be repurposed as sealing charges to collapse enemy points of entry, he reconsiders. However, he demands that the player character place the explosives, he receive the detonator, and Valdez remain to hold the barricade.

Rahmani agrees to his price to hold the Brotherhood together a while longer, which causes Valdez to recoil - but she quickly agrees and focuses on helping the wounded and marshalling the initiates. What follows is a long gauntlet through the caverns and mines below Fort Atlas, with Rahmani and Shin providing fire support and bantering. They are both very effective tanks and fire support, particularly Rahmani with her Gatling laser. On the way, they will comment on the player' character's choices in preceding quests, such as dealing with raiders and Pierce. The venture terminates in a large excavation chamber, where one has to find four entry points and place Valdez' bombs on the support girders. These are located in mining tunnels and will continue to spawn super mutants as long as they are active.

Once all four are placed, one simply has to retreat to the overlook in the chamber and wait for Shin to blow the charges. Once that is done, all that remains is returning to the Fort Atlas main area. Rahmani, Shin, and Valdez will be in the command center. The scribe will be shocked when Rahmani's actions and destruction of the transmitter are revealed to her. However, due to the appearance of the super mutant threat, Shin will reluctantly agree that unity is necessary and agree to cooperate until the threat is destroyed - at which point, he will promise to deal with the oath breaker and restore the Appalachian chapter to its proper course. Once the dialogue is over, the Steel Dawn quest line ends and all three can be interacted with to receive insight into their attitude.

Behind the scenes
The quest's name is a reference to the common saying "the best defense is a good offense," which has been applied in both military combat and sports.