The M13 submachine gun is a Paternian closed-bolt, blowback-operated 9mm submachine gun. It was made in response to a Paternian Army requirement for a submachine gun in 9mm Parabellum in order to replace the M9 submachine gun, a weapon in .45 ACP. This was concurrent with the adoption of the Browning Hi-Power as the standard-issue sidearm. Rocker Arsenal, KRIEG, and Carlton Arms submitted their proposals, the M13, M20, and M30, respectively.

Despite its mediocre performance and poor reliability in trials, the weapon was accepted and put into service over the complaints of the testers. In combat, its reliability was very poor, prone to frequent jamming and parts breakage. Soldiers referred to the weapon as the "Jam-o-matic". This was traced to construction shortcuts used by Rocker Arsenal in order to keep the price low. In addition, several senators apparently received money from Rocker Arsenal, resulting in the impeachment of said senators and a fine of $20M dollars to Rocker Arsenal.

The weapon was later upgraded to the M13A1 standard, which basically reworked the whole weapon, and Rocker was later sued for $1.5M dollars to twenty families for their deaths in combat, which they attributed to the weapon. Despite the vast improvement of reliability with the M13A1, the weapon could not shed its reputation for unreliability, and was soon replaced by the M20 in Army service and the M30 in Navy service.