"Tour of Duty"
I think this is apt and reflects not only the mission arena idiom whilst the name has a "heritage" within AH......
"Campaign"
Simple, punchy, sits easily with the other name "Classic" whilst also being able to place the player in any theatre of war.
Both reflect an arena/game/product that requires the player to return and participate to progress, both have actual RL conitations, both carry subconcious "tags" that bring to mind the adventure, challenge, glory, honour of the simulation (rather than the blood, guts, misery, loss, sacrifice of RL)
If I was wanting to put this on the shelves of the gaming shops with a bigger off line AI component then I would go for "Campaign" and "Classic" as a double box.
If I was expanding my online offering with a new product whilst enhancing the old one, then maybe "Tour of Duty" would be more appropriate.