Joined to the Hawaiian Islands by ocean currents and winds, Kalama Atoll (named Johnston by the United States) emerges from the sea 825 miles southwest of Honolulu. Over a period of 165 years, in furtherance of the U.S. imperial project, Kalama has been rendered both conservation frontier and island laboratory for an extraordinary amount of nuclear, biological, and chemical weapons. This article examines U.S. imperial governance at Kalama, an unincorporated U.S. territory, and how military ruination of Kalama has produced new military natures that call for observation and protection. Introducing a rubric of “conservation by ruination,” we highlight how a coalescing of toxic destruction and conservation efforts functions as a continuous geopolitical claim to the atoll, and how imperial formations at the atoll are weaved through technoscientific and multispecies assemblages. In essence, what is conserved in conservation by ruination is not wildlife, habitats, or nature, but empire itself. Kalama is a post-apocalyptic cyborg assemblage of bleached coral skeletons and radioactive debris, dioxin-laden leachate and crazy ants; a cacophonous ecology of weathered concrete and rusted metal, inhabited by seabirds and steadily dissolving into the sea. But it is also an atoll that remains connected to the islands and peoples of Oceania, and which is neither lost, small, isolated, or ruined. We therefore end the article by speculating on restoration of this atoll whose imperial formations capture not only its spaces, but also its futures.