Guerrillas (from "raiding party, skirmish" in Spanish) are irregular Spanish soldiers who were politically motivated to fight against the French invasion.
Historically, they usually operated in small groups to harass and sabotage the enemy troops.
These are units with weak hand-to-hand combat indexes but decent firepower.
However, since guerrillas are not part of the regular forces, it is impossible to attach an officer staff to their squads.