This helmet was given out as a promotional item in December 2012. Now the Battle Damaged Hunter can be purchased with Zen from the Customization Menu.
This helmet could previously be won through the "RARE HELMET LOTTERY BOX", which was available post-Parity Patch, untill it was removed in the holiday update on the 18th of december, 2015.
In-game Description Edit
Heavy helmet. A battle-damaged version of the Allied R21V HUNTER.