This chapter examines the legal history of public lands in the US West reserved for military use by president Franklin D. Roosevelt during wartime. Military land withdrawals ordered by FDR followed territorial precedents: nature reservations (national forests, national monuments, national wildlife refuges) and Indian reservations. Over the long nineteenth century, the management of war (including wars against Native peoples) and the administration of western lands each made the executive more powerful. During World War II these related realms of power amplified each other exponentially. Military reservations persisted after the end of FDR's wartime emergencies. Their persistence on the federal map into and beyond the Cold War is an underappreciated legacy of World War II. The story of how these reservations came to be, and continue to exist, offers insights into US expansionism at home and abroad.