The Atomgrad Special Ops Raid is a cooperative Special Ops mission that takes place in an Urzikstan underground bunker after the events of the Modern Warfare 3 campaign. Unlike the Special Ops mission included at the game’s launch, the Atomgrad Special Ops Raid requires a Raid Key to unlock.
Fortunately, there are three methods to obtain a Raid Key, which are viable across the game’s multiplayer, Warzone 2.0, and DMZ modes. You can either:
Meet any of these requirements, and you will be rewarded with a Raid Key that can access Special Ops Raids for a full week. Also, only one player in the group of three needs a Raid Key to unlock the cooperative mission.