Uses
In a military setting, machine pistols are issued as personal defense side arms to paratroopers, artillery crews, helicopter crews or tank crews. Government security service bodyguards for VIPs and heads of state who need a weapon that can be concealed under clothing may have a fully automatic machine pistol as a side arm.
Historically in western armies, and in many contemporary armies, the issue of a side arm in the form of a service pistol is a clear sign of authority and is the mark of a commissioned officer or senior NCO. In the protocol of courtesy, the surrender of a commander's side arm is the final act in the general surrender of a unit. If no ill will is meant, and a strict interpretation of military courtesy is applied, a surrendering commander may be allowed to keep his side arm in order to exercise his right of command over his men. Similarly, many commanders on a local level have been anecdotally cited as having used the threat of their side arms to motivate troops, to varied effect.
Read more about this topic: Side Arm