Fallout 4 Battle of Bunker Hill

Choices and Consequences: Informing the Railroad and Brotherhood of Steel

The Battle of Bunker Hill takes place after Synth Retention. You are given the quest to recapture escaped Synths and return them to the Institute. However, as the quest dialog points out, you have the option of informing the Railroad and Brotherhood of Steel. This is a fairly simple quest if you do neither of those things. This guide will teach you the various outcomes, and how you can score loads of loot without damaging your reputation with any of the involved Factions.

Informing the Railroad
Travel to the Railroad and speak to Desdemona. Her task for you will be to kill the Courser that escorts you to Bunker Hill, in order to free the Synths.

Informing the Brotherhood of Steel
Head to the Prydwen and speak with Elder Maxson. His task for you is to kill the Synths, in order to send the Institute a message.

Inform No One
This makes the quest just about the same - just go with the Courser and get the Synths, speak with them and use reset codes. I preferred the messy route, and you may as well. It seemed there were more fighters present when informing both factions. Inform who you want, you'll have a 3-way fight that is very action-packed no matter what you do. You'll get loads of loot from the dead, I recommend spilling your guts to both factions and killing those who have nice weapons.

Before you Go

Clear out you and your companion's inventory so you can carry as much as possible. I recommend not taking X6-88 if you plan to make everyone fight. This way, you can carry more. When I fast traveled away from here, the rest of the loot disappeared and you can only carry so much. Focus on weapons first (Gatling laser and Gauss Rifle), then BoS Power Armor. You should be able to get several fusion cores and plenty of cells for energy weapons. Don't bother with railroad armored clothing, as it can't be broken down.

The Battle
As soon as you meet with the Courser, he will call for backup, knowing an ambush is waiting. The Brotherhood of Steel and Railroad will be there, and you'll be in the thick of it as all three enemies fight it out.

I have to wonder if Bethesda will not patch this in the future (watch notes for changes). At the moment, so long as you're 'in' the Railroad and Brotherhood and have completed their entry quests, you will have 0 hostility during this mission. Yes, if you engage any of the factions in combat you will not trigger hostility. Plus they show up no matter what you do, despite them saying things like, "Our intel said nothing of the sort". I encountered hostility ONLY whenever I killed enemies that were not in combat at all. It's a prime opportunity to get XP and loot, if you don't mind exploiting a potential bug.

Should you Kill the Courser?
I like this - he has decent loot, and you're actually the only one who can kill him. He's on a rampage and can't die, unless you put a bullet in his head. I chose this route - this is the thing that really puts you in jeopardy of losing your spot in the Institute. IF you do NOT kill him, you can eventually work your way to the Synths.

Deal with the Synths
Really, after the Courser is dead, you're told to speak with father on top of CIT ruins. You cannot complete the quest for the Brotherhood OR the Railroad. You can go toward the Synths, who are hiding in a sewer, protected by turrets (hostile to all) and railroad (not hostile) while Institute Synths fight it out and try to get more loot, but it's not even really worth it. I'd say let them live. For the record, I did kill them on a 2nd attempt, and couldn't turn-in to the Brotherhood nor did it impact my relationship with the Railroad. I also went through with the mission without informing anyone and returned the Synths to the Institute. Same outcome.

Speak with Father at CIT Ruins
You should've already been here, there may be fighting but Synths should be involved and on your side. Go to the right when you first enter, and find the staircase that isn't leading up to the balconies. It's a much wider staircase. There you'll find a door which leads to the roof. Don't wander the CIT building for 10 minutes like I did.

This is all assuming you killed the Courser. You can retain your relationship with the Institute so long as you choose NOT to say that you let the Synths go. 'It was my fault', 'ambush', and 'does it matter?' all lead to the completion of the quest and the beginning of Mankind-Redefined. I tested other options - there's a lot of dialog possibilities that lead to you not failing this quest, but this is the simplest way. If you do answer that you let the Synths go, then you are banished from the Institute and now can only complete the game with the Brotherhood of Steel or Minutemen (being banished in various ways is the only way to finish with the Minutemen).