The solo campaign features four-player jump-in co-op, which includes its own particular set of challenges.
At this time, it is unknown what these particular challenges will be, whether specific objectives, or just the same old single player with the added challenge of coordinating with others. Also unknown is whether the co-op will be online or local, or both. Given the bad news we've reported as of late regarding co-op in upcoming games, we certainly hope HAWX maintains the high co-op standards of other games in the Clancy universe.