"Extremely effective! Well... Unless the enemy has a cold."
The Gas Grenade is an unlockable Equipment which can be used in one of the three equipment slots available per Trooper. Upon impact gas grenades all troopers in the Area of Effect, dealing Damage over time. Due to undocumented differences (most likely due to enclosed cockpit), Helicopters appear to be completely unaffected by the item, even when being caught in the AOE.