The Assault SMG is a new SMG in the GTA IV DLC The Ballad of Gay Tony. It is based on the Belgian FN P90, and it is classified as a personal defense weapon as it features a cartridge size somewhere between a pistol round and an assault rifle round (the P90 uses the proprietary 5.7x28mm cartridge). It is outfitted with a functional suppressor as minimal muzzle flash is produced when the weapon is fired, however it cannot be used for stealth attacks. It is perfect in gunfights and easy to carry due to its light and compact size. It is more accurate than the SMG and holds 50 rounds per magazine, however it has less stopping power and takes longer to reload. Unlike other SMGs, the Assault SMG cannot be used by the driver of a vehicle. NOOSE's Tactical Response Unit and the FIB use this weapon against the player in addition to their regular SMGs and Carbine Rifles.
- A bullpup configuration has the action and magazine of the weapon located behind the trigger to reduce the overall length and weight of the weapon.
- Under normal circumstances, the Assault SMG is not meant for the player to use in drive-by, but a glitch involving cheat codes may make this possible. If the player uses the "Advanced Weapons Set" code while in a vehicle with a different SMG selected as the current weapon, the player can then use the Assault SMG for drive-bys, however using the gun this way is rather cumbersome.