The Hei Gui Chinese Stealth Armor is an armor originally worn by the elite ChineseCrimson Dragoon troops, as well as the Black Ghost counterinsurgency/terror units before and during the Great War.
The armor has active camouflage systems that, when the player is crouched, generate a modulating field that transmits the reflected light from one side of an object to the other, making a person much harder to notice (but not completely invisible). This technology was the basis for the unstable "Stealth Boy" wrist units developed in the U.S.
The Hei Gui Stealth Armor was originally going to appear in Van Buren, the canceled Fallout 3 by Black Isle Studios. It was the step up from UAF armor with its small stealth bonus.
It also appears in the Operation: AnchorageFallout 3add-on pack. It is obtainable from the sealed armory inside the Brotherhood Outcast Outpost once Operation: Anchorage has been completed. Once worn it will increase your Sneak skill by +15 and if crouching, will also apply a +5 stealth field which can be seen in 3rd person view. It can be repaired using Recon Armor. You are also allowed to equip any headwear. Any headgear that you equip will be invisible when you go into sneak mode with the Chinese Stealth Armor equipped.