an important purpose of the side arm is to be used if the primary weapon is not available, if it has run out of ammunition or if it malfunctions. many special forces soldiers armed with an assault rifle or carbine like the m16 or m4 may also have a semi-automatic pistol as a side arm. pdws are often issued as personal side arms to combat personnel who operate in cramped spaces in which an assault rifle or carbine would be impractical, such as artillery crews, drivers, helicopter and aircraft crews and tank crews.