This is a free interpretation of the chapter art for Marathon Durandal and Marathon Infinity, portrays an officer with a heavier armor and some extra gadgets that we don't see in game.

This model is based on the art from the three games and a recent post in Bungie's twitter, that features the Cyborg, Master Chief and Oni's protagonist in a single drawing.

The Defence Drones were a key element in the defence of the UESC Marathon, their only appearance is on board the ship, as they are never seen again

Vaccumm enabled BOBs were not seen in Marathon Durandal, but they appear in that same time frame in Infinity. Their suits were probably designed by Durandal's S'pht as well as their weapons. All of them are volunteers, given the chance to either become lab rats or kill Pfhor.