Paladin Jensen is a member of the Brotherhood of Steel. He is located within Fort Bannister and has been taken captive by the Talon Company Mercs that reside there. When the player finds Jensen, he reveals that him and his squad were to launch an assault on the base. He was to scout the base before-hand but was captured as he began to do so. If the player releases him, he will charge into the lower section of the base, usually dying in the process. Soon afterwards his squad will appear and are heavily armed.
If the player clears the Fort, the underground section and kills Commander Jabsco before releasing Jensen, his squad will appear and are armed with heavy weapons, such as a Minigun and a Missile Launcher. They will then claim the base as their own and it will become a Brotherhood of Steel Outpost.
It is also possible for the player to find Jensen's squad of Paladins before entering the Fort. They will tell you that Jensen went ahead to scout and never returned. You can tell them that you will scout out the area, or you can convince them to launch their assault on the base. Usually, they will die without the player's assistance.