The following is based on Van Buren and has not been confirmed by canon sources.
We have a whole bunch of problems! Something's wrong with the generator, and I can't fix it because I'm locked out! I went to go get the floating eye bot to fix it, but something's wrong with him, too!
Vault 1 was constructed nearby a midwestern city, with an easy-to-access entrance in a cliffside close to the outlying streets of the town. It seems to have been the first vault commissioned within Vault-Tec's Project Safehouse, following the wild success of the Los Angeles Demonstration Vault.
During the Great War, the military escorted residents to the vault, with Corporal Armstrong personally escorting one individual to the shelter. The vault was in a disastrous condition, with the overseer having not yet arrived, and an underseer named Frank temporarily taking his or her place. In addition, the life support systems were down, the generators were not being supplied with enough power, and the resident floating eye bot was damaged. A new resident fixed the broken systems and brought the vault into working order.