Captain O'Shea commands the freighter Huron in The Pirates of Orion, carrying dilithium and the drug needed to save Spock's life when Orion pirates attack his ship.
O'Shea appears in the Animated Series episode The Pirates of Orion. He is master of the SS Huron, a cargo vessel hauling dilithium, which is asked to pick up a supply of strobolin and meet the Enterprise.
The drug is the only cure for choriocytosis, a disease that is harmless to humans but will kill Spock within days. Before the rendezvous an Orion ship overhauls the Huron, cripples it and strips its hold of both dilithium and medicine.
The Enterprise finds the freighter adrift with O'Shea and his crew hurt but alive. His account, and the Huron's sensor records, put Kirk on the trail of the raiders, who would rather destroy themselves than let their government's official neutrality be exposed.