An ancillary weapon is a weapon used for secondary or auxiliary purpose, such as a bayonet, combat knife or an officer's side arm. Through until the 19th century, an officer's side arm was typically a sword or saber, changing to a revolver between the late 19th century to World War I and since World War II, a semi-automatic handgun. Some soldiers such as Special Forces soldiers whose main weapon is an assault rifle may also carry a pistol as a side arm.