Located underneath Malden Middle School, this vault was presented to the public as a safe place for children in the school to take cover in the event of a nuclear war. When the bombs eventually fell in 2077, every designated family with a student attending the school, along with the teachers, made it to the vault in time. Upon entering, the children were separated from their families and escorted to the atrium, while the adults were executed by security staff, under the guise they were receiving "orientation." This act of murder coincided with the purpose of the vault, which was to enhance the gene pool of its selected residents to create stronger and more intelligent subjects. The surviving children were harshly tested mentally and physically - bordering on torture, and without regard for the survival of weaker individuals - as part of the experiment.
They were raised learning about the horrors of "Uptopland," a nickname for the wasteland, and were told that they would be strong enough to venture out into the wastes and help the suffering people upon graduation. If they were intelligent and physically well built, they were either "harvested" for their good genes when they turned eighteen, or those displaying good intelligence and obedience were recruited to the vault's science team after graduation. The others who were deemed insufficient to the vault's standards were killed upon reaching the age of eighteen after a ceremony "celebrating" their graduation. However, details found in the various terminals suggest that even those who were "graduated" were killed after harvesting. The mission of Vault 75, above all, was the refinement of human genetics.
At some point the vault was opened and emptied. Some internal log entries suggest there was a rebellion among the junior test subjects, aided by a "graduate" scientist. This is backed by the way the bodies are placed in the Vault, indicating a quick and merciless breakout. Whatever the case, in 2287 there are no residents remaining, and the vault is serving as a hidden Gunners stronghold.
The entrance is a standard vault entrance, accessible through the Malden School basement door from the wasteland. An elevator will take the player character down into the actual vault. Entering the elevator will activate the quest Vault 75. The entire vault is initially heavily populated with Gunners, although depending on the player character's choices in the endgame, other enemies will appear: Brotherhood of Steel forces will appear if the player completes the game with the Railroad or the Institute, whereas synths will appear instead if the player sided with the Brotherhood of Steel or the Minutemen.
The vault is divided in three sections, the common, lab and admin area. To access the lab and admin area key cards are necessary to unlock the security doors. Downstairs is a combat simulation room, where you can use the terminal to initiate a combat training game and record your score online. This room also contains the Gunner commander that has a lab access card.
The admin section of the vault can be found deeper in the vault behind the sealed lab doors. Some of the doors that lead to the vault overseer room within this section require an admin access card, which can be acquired/looted from one of the enemies lurking within.
- Vault 75 lab access card - On the Gunner commander in the simulation area, or in the tool case next to him. Gives access to the lab section.
- Overseer residence key - On the Gunner commander
- Vault 75 admin access card - On a Gunner in the lab area. Gives access to the admin section.
- Science bobblehead - Accessible with the lab access card, in the same room as the Gunner holding the admin access card, on the desk overlooking the subterranean combat simulation area and the "diner." From the elevator it's through the first lab access door on the right marked Security, then right again, up the stairs and all the way to the westernmost part of this floor.
- Grognak the Barbarian issue #5 - In the room just off the overseer's room (Expert pick or use the overseer's terminal to unlock)
- Vault-Tec lunchbox - On the lower level. Immediately after exiting the elevator, look left at the intersection behind the blue container. There is a skeleton wearing glasses and holding it.
- Overseer safe key - In the room just off of the overseer's room (the safe has a lock with a Master difficulty or one can use the overseer's terminal to unlock the safe).
- Vault 75 does not have an external terminal to open the vault door from the outside.
- Fast traveling to Vault 75 after the cell has refreshed may place the Sole Survivor directly on top of a fragmentation mine.
- There are three instances of four wooden blocks arranged in the name "Gary," a reference to Gary clones from Vault 108 in Fallout 3; One in the western residential room on the mezzanine floor, another under the open vault door behind some crates and one more in a cabinet inside one of the children's dorm rooms.
- The chief scientist's terminal references Stanislaus Braun from Vault 112.
- The chief scientist's terminal states that the most recent graduation was scheduled for 999.66e33 days ago. This is either a mistake or a glitch in the terminal, as this would equal 2.737×10^33 years, or over two and a half decillion years.
- When one participates in the combat simulation in Vault 75 their name and time will be recorded on the terminal in the same room.
- If you have already completed the game with The Institute, or the Railroad, there will be a battle between rogue BoS and the Gunners taking place in Vault 75. Similarily, if one completes the game for the Brotherhood or Minutemen, there will be a battle between synths and Gunners.
- Vault 75 along with Vault 95 are the only two vaults where players are unable to obtain a vault suit.
Vault 75 only appears in Fallout 4.
PC Playstation 4 Xbox One It is possible that the quest does not trigger upon entering Vault 75, therefore causing the key cards not to spawn and making the Science bobblehead unobtainable. This may be caused by a misc quest pointing to the chems stash in the vault. On PC this may be fixed by spawning the required keys (001a58a2 and 001a58a6) to allow further progress; the quest may be added and completed automatically when leaving the vault or the quest may trigger when leaving the admin area and completed upon accessing the Overseer's terminal. This can also happen even if you got the "Search for Caps in Vault 75" miscellaneous quest.[verified]