On October 25, Sergeant Platner volunteered to take atmospheric readings outside the base. Maxson ordered his soldiers and their families to prepare to vacate the base the next day. As Maxson was halfway through prying the story from Head Researcher Leon Von Felden, the facility lost contact with the outside world as nuclear weapons started to drop. On October 23, 2077, the Great War struck. He hoped to prevent a full mutiny by offering his troops a semblance of justice. On October 12, when Maxson had to step in to prevent one of his subordinates from killing a member of the science team, he ordered interrogations of the science team under his authority as acting commander. Captain Maxson was the only officer left to handle the deteriorating situation.

This prompted a nervous breakdown in Colonel Spindel, who locked himself in his office. The soldiers stationed at Mariposa discovered the fact that the scientists under their care were performing experiments with the Forced Evolutionary Virus on military prisoners. The situation unraveled shortly before October 10, 2077. They were not informed of the nature of the research. The security team was transferred to the newly constructed base as well, to provide protection for the research going on within the facility. On January 7, 2077, all FEV research was moved to the newly constructed Mariposa Military Base to commence testing of the virus on human subjects. The United States Defense Department, fearing international espionage, moved a military team under the command of Colonel Robert Spindel and Captain Roger Maxson onto the site to secure and oversee the project, now dubbed the FEV ( Forced Evolutionary Virus) project.

In 2076, the NBC division of West Tek achieved breakthrough results in the Pan-Immunity Virion Project. Main article: Brotherhood of Steel (Lost Hills)

Though small, the Brotherhood has been an influential group in the history of the wasteland, first as a survivalist group, then a major research and development house, then finally as an enemy of the New California Republic, fighting a war against the New California Republic on the west coast. While the goals of the Brotherhood vary from chapter to chapter, they share a core mission centered on seizing and regulating pre-War technology throughout the wasteland. The Brotherhood has its roots in the United States Armed Forces, founded by a United States Army security team stationed at Mariposa Military Base before the Great War.

Brotherhood of steel in fallout 4