Extraction Operator Achievement
Completed all of Charlie Cole's 4th Echelon Missions
Charlie's missions can be done solo, or with a partner via LIVE or split-screen.
These missions can be launched by speaking to him inside his workshop in the Paladin or from the SMI's Multiplayer Menu. His missions are the complete opposite of what Grim has to offer. Charlie wants you to defend your location in and around the Embassy until you're ready to extract. Each of his four missions have 20 waves of enemies, but you can extract after every five waves.
You do not need to complete all 20 waves of each mission, however. The achievement will still unlock if you extract at wave 5 for all the missions.