The pens were discovered by Delta Squad during the Siege of Nexus. Damon Baird and Augustus Cole found them when they chased after Queen Myrrah while Marcus Fenix and Dominic Santiago fought Skorge. The Queen escaped them by getting aboard a Reaver, so Baird and Cole headed back toward Marcus and Dom. When they came under attack from Skorge aboard his Hydra, they fled back towards the pens, and got aboard Reavers to escape the Hollow.