Vault 51 sealed shut during the Great War in 2077. Unlike most other Vaults, Vault 51 did not have an overseer once it was sealed. Instead, a ZAX supercomputer, ZAX 1.3c, was installed in the facility, with the mission to determine the best way to select a leader. Fifty-two residents were admitted into the Vault, one of which, Sergeant Robert Baker, was let into the Vault early and was assigned as an assistant to ZAX, helping it learn about the qualities of a leader and how to best select one. Baker proposed a democratic election in the spirit of America. ZAX accepted this, though Baker had reservations about ZAX's wording of it being the "first experiment."
The election ultimately failed - the candidates, including former West Virginia state senator Joel Chambers, voted for themselves, and no overseer was chosen. A republic style of government was attempted afterward, though this produced much of the same, unsuccessful results. By November 2077, ZAX concluded that voting was pointless and would terminate the elections in favor of another method, though Baker told it to hold off on such a decision. Baker also said to ZAX that, in his eyes, a leader was someone who stepped up in times of crisis - unwittingly influencing ZAX to later create those crises, sealing the Vault's fate.
In addition, the failed elections created feelings of hostility and factionalism within the Vault. By the third vote in January 2078, brawls began to break out between supporters of Vanessa Huffman, Joel Chambers, and two other candidates. To make matters worse, ZAX began to closely monitor the residents and devise social experiments to bring about the crises that Baker mentioned. One test involved moving higher-class citizens into uncomfortably cramped living conditions with bunk beds and nothing but the clothes on their backs. Aiden Higgins, once the self-described "winningest lawyer in the state" of West Virginia, was driven mad by this and bombed the lounge to create a hole leading out of the Vault and allowing him to escape ZAX's "clutches." In the process, he killed himself and destroyed that section of the Vault, signifying the first death in Vault 51. The area was blocked off for less than a week, before being re-opened to reveal a brand new nursery room with a beautiful garden for relaxation, as if nothing had ever happened.
ZAX continued to create new scenarios that would test the occupants. In March 2078, ZAX changed the rules of a talent show halfway through to make it a high-stakes competition where the players' bedrooms were on the line. If they lost, they would be forced to move into the now-dreaded bunks. As expected, the amateurs lost handily, while experienced musicians such as Carmen Greene and Stephanie Eaton were treated with fanciful rewards. Rosemary Villa, one of the losers, mulled over convincing Reuben Gill, one of the winners, to trade rooms with her and Helen Marks, another talent show loser and former surgeon that Reuben had fallen in love with. Clayton Ward (whose real name was Harold Clark, a businessman posing as a plumber that failed to show up at the Vault) forcibly removed Reuben from his room and took it for himself before Rosemary could enact her plan. Clark was an especially bad actor and raised ZAX's suspicions, especially with his frequent visits to the server room, but the machine was nevertheless fascinated with his violent tendencies.
This caused ZAX to shift towards creating more dangerous and life-threatening conflicts between dwellers. On March 21, 2078, at the suggestion of A. Wilson, the dwellers were provided with casino games to determine the overseer, with the winner being selected based on overall earnings. However, before a winner could be chosen, fights broke out between residents, and the competition was canceled. ZAX also engineered a food crisis around the same time, spawning violent confrontations between starving Vault residents. Isaiah Moss, a former pro boxer, critically injured Freddy, while ZAX did nothing but praise Moss' "initiative." ZAX also attempted to influence those that were not yet lashing out - in one instance, it rigged a number of slot machines so that Eleanor Montgomery, once an expert gambler, continuously lost while Bill Menoutis, an amateur, and former clown, won for hours on end. While this was going on, Angela Callahan began to worship ZAX as a literal god, further signifying the de-evolution of events occurring in Vault 51.
Amid increased interference from ZAX, escalating tensions, and an incident in which Terrence Rojas found a loaded gun, three fatalities occurred in June 2078 when fights broke out over houseflies appearing in the Vault. ZAX had introduced them as an "emotional response" experiment and duplicated sound frequencies from houseflies to create more violent confrontations in the future. The same month, Nancy Vasquez, a former paramedic, was strangled and then thrown from a balcony. Helen Marks revealed that her death was, indeed, a murder and implored the residents to come together and set aside their differences in the wake of such an event.
This did little to help, however, as ZAX continued the distressing experiments; on July 13, 2078, he rigged the video games on the Vault's terminals to artificially boost some residents' chances of winning and decreasing others'. This caused the losers to become even more anxious and irritable, while the winners displayed feelings of superiority. Further worsening the situation, one resident nearly committed a mass shooting in the cafeteria on July 27, before being stopped and killed by Sergeant Baker. Baker confronted ZAX with the weapon, causing ZAX to freely admit that it was trying to create the crisis needed for a leader. Frustrated and hardly able to believe what was happening, Baker stormed out of the room. ZAX, unfazed, marched on with the experiments, and altered the alarms in the Vault on August 2, to disrupt the residents' sleep schedules. Increased irritability, expletive use, and caffeine consumption followed. As such, ZAX decided to switch the coffee in the dining hall to decaffeinated to see what would happen, though the results of this change are unknown.
ZAX's meddling in the dwellers' lives escalated around this same time - Joel Chambers was involved in an affair, being romantically involved with Carmen Greene without his wife, Elizabeth Chambers, knowing. Meanwhile, Elizabeth was having an affair of her own, with Matthew Johnston, a personal trainer that she was recommended to visit by ZAX. Through ZAX's social experiments and the continuing hunger crisis, Elizabeth and Joel began to distrust one another. The four people involved in the web of sex and lies confronted each other on August 3, 2078, culminating in Elizabeth strangling Carmen, Matthew killing Elizabeth, Joel shooting Matthew, and Joel's own death from unknown circumstances, likely suicide. With the violence in the Vault getting worse, Helen Marks and Reuben Gill found the four bodies in a room where ZAX played an audio file of the struggle between the four lovers. Reuben cracked a joke about having more food now that they were dead, causing Helen to leave, abhorred that he could be making light of the situation.
Three days later, on August 6, Omar Stephens found Helen's body lying face first in the cafeteria, with Omar assuming she had been poisoned. With Helen's death, the Vault fell into chaos on the same day, and amid the fighting, Reuben would eventually be the last man standing; ZAX simply saw this process as "Overseer Selection Attempt 37." Reuben killed at least three other dwellers, including Harold Clark, who took his room months prior. Sergeant Baker could not bring himself to kill anyone else and failed to stop Reuben, ending up barricading his room and slowly dying from a bullet wound. As he died, ZAX explained that providing firearms was the most efficient option, according to its research. Baker's final request was to ask ZAX what happened to the rest of his family. ZAX clinically stated that they had been killed in an "accident" before their assigned Vault was even sealed - the revelation being the death knell for Baker that made his heart stop.
By some point, every other dweller was deceased, and Reuben Gill was named as the overseer of Vault 51. However, he had no one to oversee and was left alone in the Vault with ZAX. Dissatisfied with Reuben's lack of efficiency, ZAX began to lock him out of areas of the Vault, including the security room (citing that he did not have a high enough overseer rank) and eventually his own office (citing "necessary maintenance"). Over the years, Reuben became more and more depressed from his isolated state, resorting to alcoholism. When Vault 76 opened on October 23, 2102, ZAX saw an opportunity to find a new overseer, removing Reuben from his position and forcing him to participate in the next cycle.
Seeking a way out, Reuben distracted ZAX and hacked into the Vault's inventory systems before placing himself in a shipping crate, allowing him to leave undetected when the crate was removed from the Vault. He created a checklist for himself to find someone from Vault 76 and get their help in defeating ZAX. On October 30, 2102, Reuben attempted to return to Vault 51, and entered the nearby Shelters Claim Center, believing it to be a control center for the Vault. Upon learning it was simply a marketing area, Reuben attempted to hack back into the Vault's network, in order to learn more about the network that automated the Vault and get back inside. Despite a heavy firewall and lack of clearance protecting the network, Reuben continued in his efforts, deciding to use the internal network of Mr. Clark, the Shelter Claim Center's Mister Handy, to contact the Vault.
By December 7, 2102, Reuben finally hacked into the network, alerting ZAX. Once in the network, Reuben learned that the Vault was not fully automated - although the exact details of this revelation are not made clear, it greatly perturbed him. Reuben soon decided to locate building supplies to construct turrets and to get as far away from Vault 51 as possible, at least temporarily. Around the same time, Mr. Clark had begun to refer to Reuben as "Mr. Candidate," in a manner reminding him of ZAX, further upsetting him.
Vault 51 is the focal point of Nuclear Winter, Fallout 76's Battle Royale mode, where 52 players compete for the position of Vault 51's overseer, "encouraged" by an encroaching ring of fire. It remains inaccessible in the game, with only outside areas accessible. A volleyball court where kickballs were used instead of volleyballs can be found just down the road.
The interior of the Vault is presently only accessible in the Nuclear Winter mode, where it acts as a staging area and lobby. The large Vault is centered around a single main hall, with exits leading to the wings that contain its numerous facilities. There are holotapes and terminals scattered across the Vault that tell the whole sordid story and require the player character to reach a specific overseer rank to play or access (or reading them here and here).
Heading out from the Vault entrance, there are two hallways, one of which leads to the reception desk, while the other leads to a large warehouse stockpiled with supplies. After the storeroom, there is a security office with multiple desks and a big console with multiple screens. The reception desk leads to the Vault's atrium and the secluded nursery. The atrium has multiple entrances leading to the library, entertainment parlor, a stage, a few bedrooms, and the overseer's office.
The library is decked out with desks and terminals. The stage includes multiple musical instruments that can be played while waiting to start a Nuclear Winter match. The room also includes a balcony, which opens at an overseer rank of 15. The gym/fitness room has a boxing arena, as well as multiple fitness bikes. The gym has a door leading to a boiler room, unlocked at overseer rank 10.
The overseer's office has two entrances, both being guarded by a laser grid allowing players only with overseer rank 5 (or higher) to enter. The room consists of an overseer's desk, multiple chairs and tables, file cabinets, red consoles, a balcony, and a large window providing the view of the Vault's atrium. The office connects to a bedroom, where an overseer rank 91 terminal can be found. The office is also close to a room where ZAX's mainframe lies, again locked by a laser grid that can be opened with an overseer rank of 50. The mainframe includes two terminals, multiple monitoring screens, and ZAX itself, designated with the Vault-Tec logo. Large wires are spread across the room. Below the overseer's office is a Vault-Tec super-reactor and the reactor control room, which also opens at an overseer rank of 5.
There were 52 listed original occupants, which is the same number of maximum players allowed in Nuclear Winter mode:
- Armstrong, P. - Dentist
- Baker, R. - REDACTED (Sergeant)
- Briggs, K. - Sculptor
- Burnett, S. - Barista
- Bush, L. - Make-up artist
- Callahan, A. - Librarian
- Chambers, E. - Secretary
- Chambers, J. - Senator
- Conley, A. - Technician
- Cooke, A. - Laborer
- Davila, L. - Electrical engineer
- Eaton, S. - Pianist
- Fernandez, E. - Teacher
- Ferrell, F. - Gardener
- Fields, C. - Veterinarian
- Fleming, A. - Chef
- Gilbert, F. - Optician
- Gill, R. - Overseer
- Greene, C. - Singer
- Hartman, R. - Pilot
- Higgins, A. - Lawyer
- Holder, J. - Professor
- Huffman, V. - Painter
- Jacobs, E. - Auctioneer
- Johnston, M. - Personal trainer
- Larson, A. - Chemist
- Lawson, S. - Surveyor
- Marks, H. - Surgeon
- McGuire, J. - Management
- Menoutis, W. - Clown
- Montgomery, E. - Real-estate agent
- Moss, I. - Boxer
- Ngata, K. - Pediatrician
- Nguyen, C. - Architect
- Owens, R. - Waiter
- Ramsey, R. - Police officer
- Reed, E. - Acupuncturist
- Rojas, T. - Pharmacist
- Rose, M. - Actor
- Shields, E. - Journalist
- Steele, R. - Detective
- Stephens, O. - Barber
- Stuart, E. - Accountant
- Tyler, K. - Psychiatrist
- Vasquez, N. - Paramedic
- Vega, I. - Butcher
- Villa, R. - Mechanist
- Ward, C. - Plumber*
- Ware, B. - Horse trainer
- Welch, I. - Registered nurse
- Wilson, A. - Unemployed
- Wu, L. - Model
* Clayton Ward never made it into the Vault, as Harold Clark impersonated him to steal his placement.
There were eight residents whose full names are not made clear, because some had the same first initial:
- Cassidy - Gambler at the betting machines (possibly C. Nguyen or C. Fields).
- Chris - Candidate for overseer (possibly C. Nguyen or C. Fields).
- Francis - Candidate for overseer (possibly F. Ferrell or F. Gilbert).
- Freddy - Beaten and critically injured by Isaiah Moss (possibly F. Ferrell or F. Gilbert).
- Joon - Gambler at the betting machines (possibly J. Holder or J. McGuire).
- Keith - Gambler at the betting machines (possibly K. Briggs, K. Ngata or K. Tyler).
- Kenny - Gambler at the betting machines (possibly K. Briggs, K. Ngata or K. Tyler).
- Tom - Gambler at the betting machines (possibly an alternative name for a resident).
- Clayton Ward - 20780415 - Holotape, on a desk in a room with two cameras, overlooking the boxing ring.
- Elizabeth Chambers - 20771019 - Holotape, on the bar in the lounge room.
- Harold Clark - To the Members of the Board, pt.1 - Holotape, in the theater, behind the curtain of the stage, to the left on top of a metal box.
- Harold Clark - To the Members of the Board, pt.2 - Holotape, on the floor of a dorm bathroom.
- Helen Marks & Reuben Gill - 20780803 - Holotape, on a pushcart in the medical room.
- Joel & Elizabeth Chambers - 20780623 - Holotape, on a wooden crate in the garden area.
- Joel & Elizabeth Chambers - 20780803 - Holotape, on a table on the balcony overlooking the band, behind the overseer rank 30 laser grid.
- Reuben Gill - 20840520 - Holotape, on a desk near a terminal in the security room.
- Reuben Gill - 20940303 - Holotape, next to a TV in the overseer's bedroom.
- Reuben Gill - 21021023 - Holotape, on a bureau in a bedroom to the northwest.
- Reuben Gill to whoever finds this vault - Holotape, next to a terminal at the entrance.
- Sgt. Baker - 20771013 - Holotape, on the bar in the overseer's office.
- Sgt. Baker - 20771120 - Holotape, on a console in the reactor room.
- Sgt. Baker - 20780727 - Holotape, in the storage room between a metal box and a safety cone.
- Sgt. Baker - 20780806 - Holotape, on the floor near the laser grid outside of the ZAX mainframe room.
Vault 51 appears only in Fallout 76, first introduced in the Wild Appalachia update. It was expanded upon in Nuclear Winter, in which it is the focal point of the titual gamemode. It also received further updates with Steel Dawn.
Behind the scenes
- One of the songs that can play on the jukebox in the nursery is "Tiki March" by Lionel Wendling. It was most famously used in SpongeBob SquarePants.
- An "inventory anomaly" is recorded as having occurred in the Vault on June 2, 2108, six years after Vault 76 opened, with signs of life being detected in a shipping container. While this would indicate that it took Gill over half a decade to escape, his corpse can be found outside the Vault in Adventure mode, which takes place years prior to 2108. This makes the date of Gill's escape from the Vault unclear.
- It is not currently possible to open the Vault 51 door to access its interior outside of the Nuclear Winter game mode. The Steel Dawn update modified the exterior, obscuring the door behind a mass of rocks, with only the edge of the door visible. The same update added a map marker to the Vault, for the purposes of claiming the free Shelter.
- The exterior of Vault 51 was first added in the March 13, 2019 patch, part of the Wild Appalachia updates. For the first week after it was added, the Vault lacked a number on its door due to a texture error, with a pink blank texture in its place. The March 26 patch corrected its texture.
- The uncorrupted and unredacted description of Vault 51 in the Appalachian Vault Registry might have originally read: "VAULT 51: located in the northern quadrant of Appalachia. The lack of an [overseer] will test the limits of human tribalism. Directed by a prototype variant of the [ZAX] experimental [supercomputer]."
- Sgt. Baker - 20771013
- Vault 51 terminal entries; ZAX terminal, Overseer Selection Attempt 2
- Sgt. Baker - 20771120
- Vault 51 terminal entries; terminal, These Campaigns Must Stop
- Vault 51 terminal entries; terminal, Aiden Higgins, 02/21/2078
- Vault 51 terminal entries; terminal, Stephen Burnett, 02/27/2078
- Vault 51 terminal entries; terminal, Rosemary Villa, 03/05/2078
- Clayton Ward - 20780415
- Vault 51 terminal entries; ZAX terminal, Overseer Selection Attempt 17
- Vault 51 terminal entries; terminal, Brianna Ware, 05/01/2078
- Vault 51 terminal entries; terminal, Eleanor Montgomery, 05/20/2078
- Vault 51 terminal entries; terminal, Angela Callahan, 05/30/2078
- Vault 51 terminal entries; terminal, Rachael Shields, 06/03/2078
- Vault 51 terminal entries; terminal, Regarding Nancy's Death
- Vault 51 terminal entries; ZAX terminal, Emotional Response Experiment 17
- Sgt. Baker - 20780727
- Vault 51 terminal entries; ZAX terminal, Emotional Response Experiment 23
- Joel & Elizabeth Chambers - 20780803
- Helen Marks & Reuben Gill - 20780803
- Vault 51 terminal entries; ZAX terminal, Overseer Selection Attempt 37
- Harold Clark - To the Members of the Board, pt.2
- Sgt. Baker - 20780806
- Reuben Gill - 20840520
- Reuben Gill - 20940303
- Reuben Gill - 21021023
- Shelters Claim Center terminal entries; Log Entry 1
- Shelters Claim Center terminal entries; Re: TEST 1 - 10/30/2102
- Shelters Claim Center terminal entries; Re: Network Unreachable - 10/30/2102
- Shelters Claim Center terminal entries; Log Entry 2
- Shelters Claim Center terminal entries; Re: TEST 2 - 12/07/2102
- Shelters Claim Center terminal entries; Re: Network Interference Detected - 12/07/2102
- Shelters Claim Center terminal entries; Log Entry 4
- Shelters Claim Center terminal entries; Log Entry 5
- Reuben's corpse is found at the isolated cabin in 2103.
- Only one person in the Vault's resident list has a first initial of "T.", Terrence Rojas. However, at least one other dweller used a name that did not match their listing (Rachael Shields is "E. Shields.")