In 2485 the Terran Confederacy confronted the Kel-Morian Combine at the Noranda Glacier vespene refinery at Onuru Sigma. The vespene was contaminated with hydrogen sulfide, rendering it explosive. By this point, the Confederacy believed the Kel-Morians were planning something big in that area. A detachment of Confederate Alpha Squadron led by Captain Edmund Duke and a detachment of the 33rd Ground Assault Division – Dominion section – led by Captain Arcturus Mengsk advanced on the dilapidated-looking complex, only to fall into an ambush. Many of the "abandoned" structures turned out to be strongpoints.