Ops Spec Welles is in charge of a human encampment on Tantalus. When Commander Falco went rogue, Welles was unable to stop him reaching the dormant Well of Souls.
When Able Ryder arrived at Tantalus via a Dragon Assault Ship, Ops Spec Welles was there to greet him. He informed Ryder that, in order to clear a safe path to the Well of Souls, the Na'vi defending the surrounding area would have to be terminated. He then ordered Ryder to obtain three nearby heavy demolition charges delivered earlier by "Boom Boom" Batista, the premier RDA Demolitions Expert; Welles remarked that he doesn't trust "crazy Batista and those packages of danger" enough to carry the demo-charges himself.
Welles then orders Ryder to accompany a small SecOps task force advancing towards The Great Wall, then to plant the three heavy demolition charges directly on the massive rock wall to collapse it, exposing the last major Na'vi position and rendering it vulnerable. After Ryder and subsequent SecOps reinforcements helped cut a bloody swathe through Na'vi forces guarding The Great Wall, Ryder managed to plant the demolition charges and collapse it, allowing Scorpion Gunships to fly through the resulting gap and wipe out the last Na'vi defenders with short missile barrages.
Ryder then encounters Welles again, standing beside an accompanying AMP Suit guard, amidst numerous Na'vi corpses in the smoldering ruins of a village. Elated, Welles tells Ryder that "....now we can take it to the blues!" before telling Ryder to depart for the Well of Souls immediately and stop Commander Falco, while SecOps forces secure the rest of the now-undefended Tantalus area.