Fallout: Ranking Every Vault From Least To Most Horrifying
5. Vault 51 - ZAX Unit Goes Out Of Control
Vault 51, first appearing in Fallout 76, was bound to work right from the start. Everyone knows putting a semi-sentient computer in charge of proceedings is a good idea, right? That never goes wrong.
Vault 51 is quite unique in the world of Fallout in that it was never designed to have an Overseer. Instead, the Vault was governed over by a ZAX supercomputer which was given a mission to select a suitable leader from the Vault's residents.
At the beginning, the residents tried a standard democratic election to find a leader, which ultimately failed when everyone voted for themselves. At this point, Sergeant Robert Baker informed the ZAX computer that leaders are people who step up in times of crisis.
ZAX decided to interpret this differently, and tried to make these crises to find its leader. It started making social experiments to force its inhabitants to become leaders: these includes putting high class citizens into cramped conditions with nothing but clothing, forcing a resident to go crazy and bomb the Vault.
It goes on from there. ZAX started making residents fight through casino games, started witholding food, rigged slot machines to make purposefully lose and even sent out houseflies to drive people crazy.
This all came to a head several years later, ending with violent deaths of all the residents except Reuben Gill, who then became its Overseer and became an alcoholic due to the extreme isolation.