Vault 51

Vault 51 is a Vault-Tec vault located in the Forest region of Appalachia in 2103.

Background
Vault 51 was 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 ended in failure - 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 came to the conclusion 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. The machine engineered a food crisis, 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, another tragedy struck the vault in June 2078. 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 one resident nearly shot up the cafeteria on July 27, 2078, 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'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 asking 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. He managed to make contact with someone but was killed in the wilderness of the Forest before he could return to Vault 51.

Exterior
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.

Interior
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 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.

Occupants
There were 52 listed original occupants, which is the same number of maximum players allowed in Nuclear Winter mode:

* 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 a nickname of Terrence Rojas or a nickname for another resident).

Notable loot

 * Harold Clark - To the Members of the Board, pt.1 - Holotape, on the theater, behind the curtain of the stage, at the left on top of a metal box.
 * Clayton Ward - 20780415 - Holotape, on a desk in a room with two cameras, overlooking the boxing ring.
 * Harold Clark - To the Members of the Board, pt.2 - Holotape, on the floor of a bathroom.
 * Elizabeth Chambers - 20771019 - Holotape, on the bar in the lounge room.
 * Joel & Elizabeth Chambers - 20780623 - Holotape, can be found on a bench in the garden area.
 * Joel & Elizabeth Chambers - 20780803 - Holotape, on a table on the balcony overlooking the band, behind the overseer rank 30 grid.
 * Helen Marks & Reuben Gill - 20780803 - Holotape, on a pushcart in the medical room.
 * 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, near the laser grid outside of the ZAX mainframe room.
 * 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 room to the northwest.
 * Reuben Gill to whoever finds this vault - Holotape, next to a terminal at the entrance.

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, replacing the functional door with a mass of rocks, with 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 added in the March 13, 2019 patch, part of 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]."
 * Names Joon and Cassidy on the betting billboard is a possible reference to John Cassidy.

Appearances
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.