Merge a Nuke puts you on a plot where small nukes keep spawning. Combine matching tiers into bigger ones, and those bigger nukes earn Cash every second, even while you are offline.
Spend that Cash on Spawn Tier, Max Spawn, spawn speed, and a longer Lock Base timer. Raid other players to steal Cash, hit the city when it is open, and lock your base when someone aims one back at you. Climb the merge chain long enough and your plot starts paying you for sitting still, which is the kind of job every arsenal deserves.