Readiness is a cornerstone of military service. Military readiness includes cognitive and physical abilities to train and execute missions. Previous studies among civilians demonstrate that food security is associated with cognitive function and body mass index. Therefore, food security is vital to maintaining military readiness. While no analyses have been conducted on the prevalence of food insecurity for a representative sample of the active duty U.S. military, studies of individual military installations have demonstrated food insecurity rates between 15 and 33 percent. The authors compared food insecurity among the U.S. military and civilian adult populations, using data from the 2018 and 2020 Status of Forces Survey of Active Duty Members and the Current Population Survey Food Security Supplement. A weighting procedure was used to ensure the military and civilian adult populations were demographically equivalent. The findings show that the prevalence of food insecurity was 25.3 percent among the military population compared with 10.1 percent among a demographically equivalent civilian adult population. A more severe form of food insecurity, very low food security, was estimated to be 10.5 percent of the military population in 2018 and 2020, compared with 3.6 percent of the comparable civilian adult population during this period. The findings demonstrate that the military population is at elevated risk for food insecurity and that food insecurity measures can be used to reliably construct measures of active duty service members’ food insecurity for monitoring and research purposes.