The Battle of Bunker Hill

The Battle of Bunker Hill is an Institute main quest in Fallout 4.

Detailed walkthrough
Father orders the Sole Survivor to go to Bunker Hill to reclaim some escaped synths held there under the protection of the Railroad. The player character will have backup from a courser designated X4-18. Exit the Institute and proceed to Bunker Hill.

Optional: If Shadow of Steel has been completed, the player character can warn Elder Maxson about the Institute's plans, and he will ask the player character to kill the synths when the opportunity arises. If Tradecraft has been completed, it is also possible to warn Desdemona that the Institute is on its way, which will allow the Railroad to anticipate their arrival and lay an ambush. Both groups can be warned or ignored, however despite Desdemona and Maxson saying they would have had no idea of the Institute's intentions if the player character had not informed them, all three factions will be present at the hill battling, regardless of the player character's actions.

At Bunker Hill, the battle begins only after the player character meets with X4-18. He explains the situation to the player character and calls in backup, at which point the player character can pass a hard persuasion check to get more synth relay grenades. (Note: If both the Brotherhood and Railroad were informed, this second piece of dialogue will be unavailable and the courser advances towards Bunker Hill after the first dialogue.)

The main doorway into the settlement is locked, requiring the Sole Survivor to walk around to the east (right) side of the settlement where an opened door can be found. Alternatively, it is possible to climb the trailers to the right of the locked gate and jump over the fence. The inhabitants of Bunker Hill will cower during this firefight, so it is likely that most if not all of them will remain alive (due to varying "essential" statuses), despite the free-for-all taking place around them.

Once inside Bunker Hill, there will be a small hatch leading to a utility basement behind the first counter on the left, nearest the actual monument. After following the catwalks to a room far in the back, the player character finds the runaway synths Z3-22, B2-57, Y9-15 and F6-33. Here the player character has three options:


 * 1) Option 1: Escort the Courser to the escaped synths and let him take them back to the Institute. To complete this option, proceed through the fighting to where the synths are hiding, activate their recall codes by speaking to them individually and allow X4-18 to take them back. This action will not turn the Railroad or the Brotherhood hostile (provided they are not hostile already) and will not damage the player character's good standing with either faction.
 * 2) Option 2: Kill the Courser and free the synths. In dialogue with the synths, tell them that they are free to go, which immediately turns the Courser hostile and brings up the objective "kill the Courser." If not allied with the Railroad, killing X4-18 will immediately turn the Railroad members and turrets friendly (which will be revoked if one opens fire on them. If X4-18 is killed above ground, Railroad members underground may still be hostile).
 * 3) Option 3: Kill the escaped synths. Killing them makes the Courser hostile, but killing him immediately switches the Railroad members to friendly, whether the synths are killed before or after.
 * Additionally, the player character can accept an offering of 60 caps from one of the synths. This does not affect the available choice, so it is possible to accept their money and still kill them or send them back to the Institute anyway.

Regardless of choice, a new objective will be added to report to Father on the roof of the ruins of C.I.T.. The roof is accessible from the easternmost staircase inside the main entrance of the ruins. After a short discussion about how the Commonwealth has declined, Father speaks of Bunker Hill:


 * 1) If Option 1 was taken, he applauds the player character's success and rewards them with 500 caps.
 * 2) If Option 2 or 3 were taken, he demands to know what happened. Wrong dialogue choices here, such as admitting it was the player character's fault, can lead to being banished from the Institute. Stating that it doesn't matter, or that they were ambushed, makes Father upset with the outcome but ultimately preserves the player character's good standing with the Institute.

The quest concludes, and if the player character's good standing with the Institute is preserved, Mankind - Redefined begins.

Behind the scenes
The title of this quest is a reference to the historical Battle of Bunker Hill, an important conflict of the American Revolutionary War occurring near Bunker Hill in 1775. Contrary to popular belief, the bulk of the fighting during the Battle of Bunker Hill took place at the site of the American redoubt on Breed's Hill, not Bunker Hill. The Bunker Hill Monument was erected at the site of the battle, on the peak of Breed's Hill. Thus, both historically and in-game, the Battle of Bunker Hill takes place on Breed's Hill, not Bunker Hill.

Bugs
Bitwa o Bunker Hill La batalla de Bunker Hill A Batalha de Bunker Hill Битва за Банкер-Хилл Битва за Банкер-Гілл 碉堡山戰役