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From the inside the blimp's vulnerable. To keep that baby afloat it's got massive gasbags full of hydrogen. Your job is tricky. You got to find a way to place these explosives on the gasbags.Tinker Tom

Precipice of War is a Railroad main quest in Fallout 4. It is the follow-up from Underground Undercover and is part of a chain of quests, all of which are tied together, to an alternative method of completing End of the Line.

Quick walkthrough

Railroad main quest: Precipice of War
Warn Desdemona.
Defend Railroad HQ.
Talk to Desdemona inside HQ.
Secure Old North Church.
Speak again with Desdemona, now near the church exit.
Meet Tinker Tom at the Cambridge police station.
Eliminate all Brotherhood forces.
Talk to Tinker Tom.
Defend the Vertibird.
Talk to Deacon.
Reward: 500+ XP
Leads to: Rockets' Red Glare

Detailed walkthrough

At the end of Underground Undercover, there was a warning that the Brotherhood of Steel are moving to attack Railroad HQ and The Railroad needs to be warned as soon as possible.

In fact, as soon as Desdemona is warned of the Brotherhood of Steel's impending attack, the attack begins. Defeat the Brotherhood soldiers that attack from the route leading to the escape tunnel. After they are dead, speak with Desdemona, who informs the Sole Survivor that the catacombs are the only way to escape. Glory has already gone ahead to secure passage, and Desdemona asks the player character to assist.

Entering the catacombs, Glory has been grievously wounded. Regardless of how the player character answers her, she succumbs to her wounds. Two knights— one in power armor, the other in BOS combat armor— will burst through the sealed entryway with explosives. Kill them and then continue back through the crypt, fighting initiates and knights along the way. Up on the main floor of the church, another unit of Brotherhood initiates, knights and aspirants will be waiting. They will all need to be eliminated.

Once all of the soldiers are dead, Desdemona and the others will enter from the catacombs. Grieving the loss of Glory, they note that the Brotherhood underestimated the Railroad's strength and will attack again with a much greater force, thus the Old North Church will not be safe until they are eliminated as a whole. Operation "Red Glare," the destruction of the Prydwen, is a go. To carry it out, the player character must steal a vertibird from the Cambridge Police Station. Head there immediately and rendezvous with Tinker Tom.

Outside of the station, Tom mentions that the vertibird is still on the roof and all Brotherhood personnel must be eliminated (including Haylen and Rhys). Enter the station and open fire, making sure to check every room, including the garage, which might be closed from the outside. Once they are all dead, head to the roof and kill the remaining soldiers. Tom hands over an explosive charge to affix to the tanks of hydrogen aboard the Prydwen, which will detonate and ignite the hydrogen in the envelope, bringing the airship crashing down.

While Tom preps the vertibird, an enemy vertibird will arrive and attack. Shoot it down or kill everyone aboard, then talk with Deacon to complete the quest. The quest Rockets' Red Glare will then begin.

Quest stages

Quest stages
StageStatusDescriptionLog Entry
101 Warn Desdemona
200 Defend Railroad HQI got to Desdemona in time. But the Brotherhood of Steel could attack at any moment. I have to defend my friends.
300 Talk with Desdemona
400 Secure the CatacombsThere's only one way out of the HQ - straight through the catacombs and everything the Brotherhood brought to wipe us out. I'm the Railroad's only hope.
500 Secure the Church
600 Talk with DesdemonaRailroad HQ survived. But until we destroy the Brotherhood's Prydwen we'll never be safe again. To stop them we need to acquire a Brotherhood vertibird at Cambridge Police Station. Tinker Tom will meet me there.
700 Meet Tinker Tom at the Police StationWe need to secure the Cambridge Police Station so Tinker Tom can commandeer their vertibird. That vertibird is the key to destroying the Brotherhood's flying fortress, the Prydwen.
800 Eliminate Brotherhood forces
900 Talk with Tinker TomTinker Tom's going to need time to get our commandeered vertibird flight worthy. So Deacon and I have to keep him safe until then.
950 Defend the vertibirdWith the Brotherhood forces dealt with, Tinker Tom has the vertibird ready for take off. Now I need to check in with Deacon before we board her.
1000Quest finishedTalk with DeaconWith the Brotherhood vertibird secure, we're as ready as we'll ever be to deal a fatal blow to the Brotherhood of Steel. By destroying the Prydwen.
20000Quest failedQuest Failed

Companion reactions

Promise Glory to free all the synths.LikeLikeLoveN/ALoveLoveLikeLikeLoveLikeLoveN/A
Tell Glory she'll liveLikeLikeN/ALikeLikeLikeN/A
Leave GloryDislikesHatesHatesN/AHatesHatesDislikesHatesDislikesLikeHatesN/A
Tell Tom to relaxLikeNo reactionLikeN/ALikeLikeLikeN/A
Tell Tom he's having a paranoid fantasyDislikesDislikesN/ADislikesDislikesDislikesN/A


  • If Deacon is not the current companion, he will leave whatever residence he is located at, and follow Tom throughout the mission.
  • The Final Judgment weapon can be obtained by going to The Prydwen and killing Elder Arthur Maxson.
    • He will not spawn until the three explosives have been placed.
  • The mission can be completed with "no alerts" if the Brotherhood has been killed off beforehand.
  • If Duty or Dishonor has been completed by convincing Initiate Clarke to turn himself in and he has not subsequently been let out, he will be locked up in Cambridge Police Station. Clarke is non-hostile and can be released without incident. Deacon likes freeing Clarke, who will run out of the station.
  • One may have to wait for Deacon to show up in order to talk to him. The map will show him somewhere along the route between Old North Church and the bus stop to the north of Cambridge Police Station. Attempting to quick travel to his location will only result in him being further along the route and no longer near where quick-traveled to. The Sole Survivor can sit to wait a couple hours at the bus stop and he will show up.
  • If the player character gets stuck and is unable to secure the police station despite all enemies being dead, try killing Haylen at Waypoint Echo (if the quest Liberty Reprimed had been started before betraying the Brotherhood).
  • If The Lost Patrol has been completed and Brandis convinced to return to the Brotherhood, he will be among those opposing the player character during this mission.


  • Xbox OneXbox One When trying to talk to Desdemona to warn her of the coming attack, she will only speak generic dialogue lines, and cannot be alerted of the attack. There is no known fix.[verification overdue]
  • Playstation 4Playstation 4 Tinker Tom will be sitting on the ground after taking too much damage and the quest will not progress unless he goes to the Vertibird. It will say "Defend the Vertibird," but as Tinker Tom is bugged, the attacking Vertibird will not appear to advance the quest. This can be fixed by fast traveling to another location, and then back again.[verified]
  • PCPC Playstation 4Playstation 4 Shooting the attacking Vertibird with a weapon with the crippling effect will cause the Vertibird to become indestructible - its health can be depleted, but it will not crash, thus preventing the mission from progressing to the next stage.[verified]
    • Another way to fix it is to walk around and/or back and forth below the Vertibird, this may cause it to crash.
  • PCPC Even if one shoots down the Vertibird, the quest can become bugged and not progress past "Defend the Vertibird". Entering setstage 2c8cb 11000 with the enemy Vertibird targeted will progress the quest correctly.[verified]
  • PCPC Playstation 4Playstation 4 The church may be impossible to secure even after killing all the Brotherhood members inside.[verified]
    • The setstage command also does not seem to fix this.
    • This may be caused by a straggler that is not readily visible on the first pass (perhaps due to one Brotherhood soldier being glitched into a wall or through a floor). Walking around and periodically firing a non-silenced weapon may cause the soldier to appear.
    • If Paladin Brandis is present, even though he is friendly, he may be the source of the issue, and must be killed.
  • Playstation 4Playstation 4 At Cambridge Police Station, killing some members of the Brotherhood of Steel will count towards the Murder statistic in the Pip-Boy, despite them clearly being hostile towards the player character.[verified]
  • PCPC The quest may get stuck on the "Eliminate Brotherhood forces" stage, even though they are all dead, including Haylen whether she was at Waypoint Echo or showed up at the police station. To fix this, type in the console: setstage 2c8cb 500.[verification overdue]