Vault 117

Experiment
Vault 117 was publicly announced as a vault that the entirety of Petersburg could live in with the protection of the military in Fort Lee. Vault-Tec, however, had different ideas. They told the soldiers stationed at Fort Lee that the vault was for military personnel only, and that anyone who approached it was to be gunned down in order to not risk the security of the vault. The purpose of the lie was meant to test how military personnel reacted when killing innocent civilians under the orders of their higher ups, and then having to live with that for decades.

Result
When the Great War occurred, the residents of Petersburg fled to Vault 117, believing it to be a haven of safety from the impending nuclear doom. However, they were caught by surprise when the soldiers of Fort Lee were guarding it and gunned down anyone who came too close to the fence surrounding the entrance. Some citizens, angry at being denied access, tried to race past them and climb the fence, though none of them made it as the military gunned all of them down. Before it could occur to them what they had done, the soldiers were all ushered into Vault 117, which closed, leaving them inside a sealed vault for decades, the higher ups working as the Overseers

The soldiers who had killed the residents of Petersburg sat in their isolation for decades, thinking and mourning over what they had done. The higher ups who ordered the act were firm in saying that the civilians were risking national security, yet it didn't quell the guilt felt by the 3,000 soldiers. By 2087, the population had lowered from 3,393 soldiers to 2,798 soldiers, as many of the soldiers had either taken their own lives in their guilt or had left the vault in their confusion, wandering the wasteland. Some of the soldiers wandering the wastes began trying to protect any survivors they could find, though civilization had yet to hit Virginia majorly. Five years later, in 2092, the remaining soldiers revolted against the higher ups in their grief at their act, and the anger that the higher ups had ordered them to do so. Much of the vault was destroyed in the resulting battle lasting two years, many of the lower floors collapsing due to explosives being set off. By the end of 2094, much of the population was deceased, the remaining 1,203 soldiers standing guard in the vault, protecting it from anyone on the outside in their insanity caused by the isolation. Their descendants still guard the vault, though the original reason has been lost.