Mattis returns to the mainland, where he is assigned to the Marine Corps Combat Development Command (MCCDC). There he is to use his experience of the past years in warfare to help refine the combat doctrine and tactics of the Marines.

Mattis helps to create a program focused on lower-level officers who will be fighting insurgents in the Middle East, as he sees no end in sight for that particular conflict. His concern is that younger Marine officers will not be mentally prepared for the ambiguity of urban warfare against an enemy that shoots and runs. It is as vital to know when not to shoot as to know when to engage.

Mattis uses the simulators that train pilots as inspiration. A pilot can run numerous scenarios (and “die” in them), helping to refine their skills before getting into an actual cockpit. Mattis creates a real-life “simulator” at Camp Pendleton in California. An old tomato-packing plant is used as a facsimile of a Middle Eastern town, and the Marines run various scenarios while actors and manufactured smells, deaths, etc. make it as realistic as possible. The Marines call it the “Infantry Immersion Simulator.” Mattis also brings in an unusual assortment of trainers for a program called “Combat Hunter.