|The following is based on Fallout Tactics and some details might contradict canon.|
The Assault on Osceolla was the assault of the main base of Gammorin's army in Osceolla, Missouri conducted by the Midwestern Brotherhood of Steel around 2197. It was the final confrontation of the Brotherhood and Gammorin's Army.
The Warrior's team was sent into the compound with two objectives: to eliminate Gammorin, leader of the super mutant forces in the midwest, and to save General Barnaky, previously taken prisoner during the Battle of St. Louis.
They stormed the base, killing many of the mutants inside.
Once they encountered the leader of the mutant army, the Warrior and his or her team made a shocking discovery: Gammorin was originally part of the Brotherhood of Steel, having once been Paladin Latham, but became insane following a head injury from a fight with the original Gammorin. He believed that the Super Mutants were the ideal that the Brotherhood should have been.
Gammorin spoke of the Elders' foolishness and blindness to a new menace from the west, which he claimed that only his mutants could to fight. At the end of the fight, being mortally wounded, his last words were that all he had done was in the name of stopping the coming threat.
They succeeded in their first objective, but General Barnaky was already captured by the Calculator's robot army. A letter to his wife, Maria, and a nuclear weapon control device, which would later prove to be useful with the ICBM warhead from Kansas City, were also retrieved.
With their leader dead, the mutants quickly split into factions as they had following the Unity crisis. Some turned to internal fighting as they wrestled for control, while others offered to join the Brotherhood in the fight against the Calculator. Dagger Squad continued to hunt any mutant stragglers still loyal to the army.
The Assault on Osceolla appears only in Fallout Tactics.