- “Sir, O'Brien's down.”
Battle of MombasaEdit
During the Battle of Earth, his squad was dispatched from the In Amber Clad to relieve Marine ground forces fighting the Covenant Army in New Mombasa, Kenya. Their D77-TC Pelican was shot down by a Type-47 Scarab operating in Old Mombasa. When the dropship made a hard landing outside of Hotel Zanzibar, O'Brien was killed instantly during the crash. Private Walpole noted his death after the crash.
- O'Brien is named after the Bungie employee "Bill" O'Brien, who worked on the animations and cinematics for Halo 2.