The Vault is the nickname for the United States government's Maximum Security Installation for the Incarceration of Superhuman Criminals, a recently completed facility not yet fully operational. The Vault was specifically designed and built to cope with the increasing number of convicted criminals whose superhuman powers and abilities made them difficult to imprison in conventional facilities. For years prior to the Vault's construction, superhuman criminals sentenced to serve time were sent to ordinary prisons and jails and usually managed to escape in a matter of weeks or months.

The first attempt to fashion more secure cells and containment devices took place at Riker's Island Prison outside New York City. While the rest of the prison still contained ordinary criminals, an entire wing at Riker's was modified to house special apparatus to hold superhuman beings. Although the reinforced cells were significantly more effective than conventional cells in holding superhuman criminals, relatively little could be done to suppress more exotic powers such as energy projection. Furthermore, concentrating so many superhuman beings in such a small environment increased the probability of two inmates using their powers in concert to enable one another to escape. Jail breaks, when they did occur at Riker's, were highly disastrous, enabling numerous prisoners to escape and resulting in extraordinary amounts of destruction. Normal criminals were also at high risk being incarcerated in the same facility as superhuman criminals. Finally, after numerous jail breaks costing millions of dollars to repair, and threatened legal action on the part of the families of ordinary inmates who believed they were in mortal danger from their fellow superhuman prisoners. Riker's wing for incarcerating superhuman beings was shut down and its charges scattered to other facilities. Among the criminals once held at Riker's were the Cobra, Electro, Mysterio, Whirlwind, Mister Hyde, the Vulture, the Tapster, the Wizard, and countless others.

The second attempt to fashion better ways to hold superhuman criminals was conducted at Project: Pegasus, the government's semi-secret energy research facility. One wing of the Project, "The Compound," was devoted to "human resources research," which meant the study of those with superhuman powers. Although a number of superhuman beings with no criminal records voluntarily underwent testing at the Project's Compound, most of the subjects who were studied were superhuman criminals "on loan" from various penitentiaries. The government had the authority to transfer any convict to the Project without their approval, but the Project could not test or experiment upon the inmate without his or her permission. Most inmates at the Prefect agreed to the tests in exchange for time off their sentences, Unlike Riker's, the Project was actively engaged in examining the nature of the inmates' abilities. The immediate by-product of this research was better ways to contain and even neutralize certain potentially dangerous abilities. Finally, superhuman criminals were sent to the Project just to take advantage of its containment facilities, rather than any compelling need to study them. As far as its capacity to successfully incarcerate superhuman criminals, the Project was as superior to Riker's Island as Riker's was to conventional prisons. Criminals did manage to escape their cells in the Compound on occasion (usually taking advantage of a power shutdown caused by some problem in another part of the Project), but only two criminals, Moonstone and Blackout, managed to escape the Project entirely. However, despite the presence of superhuman security people, damage done to the Project because of superhuman criminals began to creep into the millions. Finally, government task force investigated the matter and concluded that it was hazardous and cost-ineffective to house such dangerous beings in this otherwise peaceful multi-billion dollar energy research facility. Thus Project: Pegasus was ordered to phase out its human resources research and remove all prisoners from the premises.

Utilizing what was learned about the containment and neutralization of superhuman beings at the Protect, the government began work on The Vault. One of the advantages Project: Pegasus had over Riker's Island as a containment center was that few civilians knew exactly where it was. While accomplices of superhuman criminals could storm Riker's Island and aid in a jail break, this never occurred at the Project since so few people knew where it was. The government decided to keep the Vault's location even more secure than the Project's. The Project's Compound, like most of its facilities, was situated deep underground inside a mountain in the Adirondack Mountain range. The government decided to similarly situate the Vault, only in the Rocky Mountain range in Colorado. Because the purpose of the Vault is simply containment and not research, only a small part of the Vault contains scientific research apparatus, and that is only to examine prisoners to determine what is required to safely contain him or her. The government hired the team of engineers who worked on the construction of the Compound for the Vault. Working as a consultant was the weapons designer named Forge who achieved fame with his invention of a device to neutralize the powers of certain mutants and aliens. The Vaults administrators have investigated the possibility of permanently neutralizing the superhuman powers of the criminals, but so far this has been ruled unconstitutional

The Vault has been designed and built to be as close to inescapable as humanly possible. Although it would have cost in the trillions to build all of the retaining walls out of Adamantium, the most impervious metal alloy known to man, at least half of the containment area is Adamantium lined, and the rest is constructed of Omnium steel, another highly impervious substance. The Vault has 3 main levels, the uppermost of which is 40 feet beneath the ground. Surrounding the subterranean facility is the natural granite and shale of the mountains, ten feet of concrete, five feet of Omnium steel, and two inches of Adamantium Cells are modular and designed to permit easy installation of special neutralization devices required by the nature of the prisoner's special abilities.

The Vault has a five person administration board, a warden, thirty-five guards, a six member Retriever squad to escort prisoners to the facility, and a three person science/medical team who screen and test prisoners upon admission to determine the special containment facilities required. As yet, the only staff members whose identities are known are Howard G. Hardman, the warden of the Vault; Dr. Henri Sorel, head of the science team and former head of human research at Protect: Pegasus; and Michael O'Brien, former security head at the Project and now the head guard. Each of the Vault's thirty-five guards and six Retrievers wear Guardsman armor. The original Guardsman battlesuit was designed by Anthony Stark, the creator and prime user of the Iron Man armor. Stark eventually gave the Guardsman armor to Michael O'Brien for his exclusive use, and O'Brien used it to qualify for the position of security chief at Project: Pegasus When the Guardsman armor was damaged in combat, the Project administrator went to Stane International, the successor to the company that originally built the armor, to have it rebuilt. At that time, the government also commissioned Stane to begin mass production of the suit for future use at the Vault, O'Brien was not pleased by the replication of his armor, but, perturbed at certain Protect policies, he resigned from Project: Pegasus to work for the Vault O'Brien's first task was the training of the men the government selected to work as guards at the Vault. He is now in charge of the thirty-five prison guards.

Just prior to the official opening of the Vault, its containment facilities were used by the National Security Council to detain the East and West Coast Avengers pending an investigation of treason. The containment facilities proved quite effective holding eleven of Earth's most capable superhuman beings, and had the Avengers not had outside help, they might never have been able to escape. Enheartened by this test of both the facilities and the Guardsmen, the Vault's administrators began official operations the next week by transferring the inmates at Project: Pegasus to the Vault. The Vault is in the process of gathering all of the superhuman criminals currently serving time in the nation's less secure institutions. In almost all cases, the federal wardens have been relieved to relinquish their prisoners to the Vault. The Vault has a special armored personnel truck for its Retriever squad to move prisoners to the Vault.

The Vault has only five of its individual cells filled at present. Rumors of the facility have spread through the underworld community like wildfire, causing great consternation over the many mysteries surrounding it. The prevailing wisdom is that there is no escape from the Vault until you have served your time. A criminal's only hope is to escape before they put him or her in there, it remains to be seen if the Vault lives up to its reputation and design specifications.

First Appearance: AVENGERS ANNUAL #15