Combined Operator Achievement
Completed all of Isaac Briggs 's 4th Echelon Missions
Briggs's missions are mandatory COOP, but can be done via LIVE or split-screen.
His missions can be launched by speaking to him in the Paladin or from the SMI's Multiplayer Menu. These particular set of missions are more of a story-driven COOP experience, rather than simply retrieving information or fending off waves of enemies. You can approach these missions with whichever playstyle you prefer. Just remember these cannot be done solo!