"Underslung launcher mechanism designed to deliver an electrically charged shotgun slug; contact with enemy personnel results in temporary, but complete, paralysis."
W-Y 21S Arc Rounds description (from Aliens: Colonial Marines)

The 21S Arc Round is an electrically charged shotgun slug manufactured by the Weyland-Yutani Corporation for use with an underbarrel shotgun attachment for the MK221 Tactical Shotgun.


  • The 21S Arc Round launcher in Aliens: Colonial Marines is visually identical to the U1 Grenade Launcher unit fitted to Pulse Rifles as standard. Given that the Colonial Marines Technical Manual states the U1 is capable of using a variety of ammunition types, it seems possible the name "21S Arc Round" launcher is simply a gameplay designation, and that the weapon is in fact a U1 loaded with a different ammo type. The fact the 21S is named after ammunition it fires rather than having a specific designation (unlike the U1) further supports this theory.