Years after the Brotherhood Airship expeditions and the rise of the Attis Army, Rhombus, the High Elder of the BoS, began to think the new army could be a threat. During the elder council he demanded that the Brotherhood do something about them. However, the elder council denied his request. They said that the other expedition was growing by similar means (tracking down and determining the extent of the remaining super mutant threat) against Gammorin's Army. This caused a divide to form in the Brotherhood.
Rhombus didn't listen to the elder council and started a crusade against the Attis Army. With a few Scribes and Paladins, he mounted a new expedition and began to track the Attis Army. They followed the trail to Texas and it was there they discovered an abandoned vault prototype dedicated to the Secret Vault project. It was here that the main base of the Brotherhood of Steel in Texas was installed. Afterwards they began to search for information and began hiring new recruits to fill their ranks.
In 2208, Jane, the raider Matron and their contact in the town of Carbon, reported movement of super mutants there. Rhombus decided to go to Carbon with a group of Paladins to investigate. Her information indicated that their next destination would be the ghoul city of Los. After arriving in Los a battle broke out beetween the Attis Army, the Church of the Lost, and the Brotherhood Paladins. The Brotherhood group was annihilated and Rhombus was captured. Attis used the confusion to his advantage and managed to get into the Secret Vault. But to access the laboratory section required a key card, only possessed by the Church of the Lost.
Rhombus was eventually liberated by the Initiate. After this he assisted the Initiate to the truck where he had hidden the key card. Once at the truck Rhombus was severely injured by a ghoul suicide bomber. Unable to continue fighting, he gave the Initiate the key card and entrusted the task of stopping the Attis Army and finding the Secret Vault with him. The Initiate then went to the Secret Vault and trigged the self-destruct system, destroying both Los and the Secret Vault. The Brotherhood of Steel contingent was victorious and the Attis Army destroyed. Afterwards, this Brotherhood of Steel contingent probably returned to Lost Hills.