arXiv:2610.40078v2 Announce Type: replace Abstract: Military installation energy readiness depends on having sufficient resources to sustain mission-critical loads throughout a prolonged utility outage. This paper develops a method to help operators manage energy resources during normal grid-connected operation while preserving islanded readiness. A robust viability kernel identifies combinations of battery energy, fuel, and load-shifting capability sufficient to sustain critical load under uncertain demand and photovoltaic generation. A probability bound translates stochastic generator start failures and recovery into a deterministic generator count selected to meet a specified availability requirement at islanding. Case studies for a fourteen-day islanding requirement at 0.999 islanding-entry availability show that advance warning of an outage can be used to prepare resources to meet a higher readiness requirement before islanding begins. The case studies further demonstrate that economic-only operation and the evaluated fixed battery reserve policy can fail to sustain critical load for the required duration, whereas enforcing the resource-dependent requirement preserves readiness at a modest increase in modeled grid-connected operating cost. These results demonstrate how active resource management can preserve long-duration energy readiness. The framework also helps commanders understand how readiness changes with operating conditions, even when the available resources remain the same.