The mutant army was a plan that Dr. Noah had in mind for years. It consisted of an army of genetically mutated creatures, some that were mindless animals and some that were smart enough to use weapons.
The beginnings of the army occurred in 42 BBY when Noah unleashed a bunch of monsters on the MI5 operatives that were aboard his space station Noah's Ark.
But in 34 BBY, the plan was a bit more organized. Noah had planned to unleash the creatures upon MI5 Headquarters, but the MI5 agents caught up with him first, so he instead let them loose on them. The mutant army battled the time traveling MI5 droid agent QUAD in Noah's lab on Khubeaie. QUAD won that fight and all the mutants were destroyed.