Increasing threats to the electrical grid are generating responses that seek to secure selected “mission critical” assets essential to the functioning and continuity of life. Focusing on military and urban domains in the United States that use the smart microgrid as a technique for securing “always-on” power during grid failure, we explore the core rationales, socio-technical configurations and wider implications of these projects. The paper argues that smart microgrid systems are an adaptive mode of grid expansion that utilizes the off-grid “islanding” and grid-tied functionalities of microgrids to secure urban operational continuity. They constitute a relational systemic reconfiguration that draws on, develops and holds together expertise and interdependencies across domains to construct an integrated response to grid vulnerability. Smart microgrids thus bring into view an emerging set of spatial–temporal dynamics and implications through which the interval of disruption is eliminated and power maintained, albeit for selected designated critical assets.