The M8 submachine gun was a bullpup, air-cooled, gas-operated weapon used by the United Nations Space Command during the Swarm War. A selective fire personal defence weapon, the M8 was designed and manufactured by Hall Munitions in response to a UNSC request for a replacement for the 5x23mm high velocity armour piercing cartridge. It was designed as a compact but powerful firearm for vehicle crews, operators of crew-served weapons, support personnel, special forces and counter-terrorist groups. Key requirements for the initial specification included accuracy to a minimum range of 350 metres in a weapon no longer than 700 millimetres, and the capacity to reliably penetrate Swarm armour at this range.