In a curious incongruity, the planet's dominant fighting machine, the US military, has taken on a largely unrecognized yet crucial role in preserving California's cultural and ecological treasures. Recruits learn to spot murder holes and fire assault rifles amid one of the most biologically diverse regions in the world, and researchers look to the desert's flora and fauna for inspiration. Environmental stewardship is law on installations throughout the United States, but a few bases in Southern California have taken a more comprehensive approach-one in which energy security and protection of natural and cultural resources are embedded in the concept of national defense. Unlikely Ally takes us through these bases to examine Camp Pendleton's colony of endangered terns; the creation of wildlife corridors by the Marine Corps Air Ground Combat Center in Twentynine Palms; the Department of Defense's research on the desert tortoise in the Mojave; innovative water conservation practices at Fort Irwin; clean-burning rocket fuels developing at China Lake; and other strategic imperatives given a geopolitical landscape easily destabilized by climate change. With journalist Marilyn Berlin Snell as our guide, we explore a culture informed as much by the natural world as by human ideas of leadership.