The unit, newly created and innovative in nature, was facing its toughest test yet — a 10-day mock battle across Southern California, where a series of military bases played the role of an island chain. Though outnumbered by the regiment it was fighting, the team from Hawaii had an edge.

The team was built to fight on islands and along coastal shorelines, the "littoral region" in military parlance. It had also been given special equipment and the freedom to innovate, developing new tactics to figure out one of the service's highest priorities: how to fight a war against Chinese forces in their own backyard, and win.

Although far from the ocean, the base at Twentynine Palms offers about 1,200 square miles to train, more than all of the Marine Corps' other training bases combined. Days ago the two sides were dropped off here about 12 miles from each other. Then it was time to fight.

No live ammunition was used, but that was essentially the only rule. Evaluators alongside them graded everything they did, assessing hits and misses and pulling troops out of the action when they had been "killed."