According to the Creation Club description, the armor hails from a space marine who used it against the forces of Hell, and has now somehow made its way into the Sole Survivor's inventory for use in the Commonwealth.
While the armor itself is similar in tone and shape to a form of combat armor, there are distinct differences. The helmet is closed and has a reflective visor. The green shoulder pauldrons are attached to the chestpiece by some form of cable. The chest piece itself is stylized to look like a muscular torso and ending at the rib cage, the center of which has three claw marks. The fatigues worn under the armor are a darker green and heavily torn, exposing the wearer's stomach and leg. The belt has two small satchels, one at each side. The armor also comes with black gloves. Gray bulky kneepads are worn in addition to brown boots.
Initially, this armor could not be modified at an armor workbench. A patch changed the armor so that it was no longer at full strength initially and required extensive modification to get back to the original, extremely high levels of damage, energy, and radiation resistance.
Deposited into inventory after installing the "Doom Classic Marine Armor" creation.