Based on the Belgian FN P90 personal defense weapon, the Assault SMG is one of the first bullpup weapons offered in the GTA series. In real life, the P90 uses the proprietary 5.7x28mm cartridge; however, in-game, it shares its ammunition with other SMGs, similar to other weapons sharing ammunition despite different cartridge sizes. 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 as firing the weapon out in the open attracts attention.
The Assault SMG is perfect for heated gunfights, having greater accuracy and a higher magazine capacity than the Standard SMG; however, it is more expensive, has less stopping power, a real-life criticism of the P90, and has a longer reload time. Unlike other SMGs, the Assault SMG cannot be used by the driver of a vehicle under normal circumstances (see #Trivia).
Despite its name, the Assault SMG doesn't fit very well for assault roles due to its low damage, but it should be used for longer distances where its high accuracy and capacity give it an edge over other SMGs or pistols, but remains outclassed by assault and sniper rifles.
- Gay Tony gives Luis an Assault SMG en-route to the Dragon Heart Plaza during the mission "Chinese Takeout".
- NOOSE's Tactical Response Unit and the FIB use this weapon against the player in addition to the standard SMG, Carbine Rifle, and the Automatic Shotgun.
- Armando sells the Assault SMG for $6,725 plus $150 for each additional 50 round magazine.
- If the player uses the "Advanced Weapons Set" cheat 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 in this fashion is rather cumbersome.
- The beta version of the Assault SMG, seen in the debut trailer, lacks the suppressor and has a different firing sound. Additionally, the filler/foam in the Assault SMG's gun case in Armando's SUV does not have a cut out for the suppressor.
- Strangely, the used bullet cases are ejected from an invisible ejection port on the side of the gun instead of the real one under the handgrip.
- Luis refers it as 'some sci-fi shit', which can be heard in Chinese Takeout.