The Secret Vault, built by Vault tec and made exclusive for high ranking Vault Tec members, was made to preserve the company and allowing them to return to the wasteland alongside the Enclave with all the necessary technologies and materials.
It was a major production and research facility, and contained many technological artifacts. This vault was used to research new technologies to benefit them in the post nuclear world including employing its own strain of FEV, working on biological weapons, testing animals, and creating robots to control the vault's systems.
Eventually however, CALIX, the supercomputer in charge of controlling the security robots, malfunctioned, a civil war broke out in the name of what was humane, and many of the experimental creatures escaped, wreaking havoc on the vault. It is eventually destroyed when its nuclear reactor is detonated.