"Allows the use of Graviton Body Armor. Graviton Body Armor offers improved protection from knockback and stun effects. These protections are improved with better training and are based on the number of pieces Graviton Body Armor worn. In addition, higher skill improves the armor's recharge rate based on the amount of Graviton Armor and the skill pump level."
Graviton Armor is the game's heavy assault armor and is capable of taking an incredible beating. Combined with the resistance to stun and knockdown, this makes Commandoes and their branch classes the ideal frontline troops. However, it has less regen than most armor types, making it unsuited to protracted combat without support; increasing your Armor skill rank compensates for this by improving your regen rate.