The National Guard (NG) served as a critical component of the US COVID-19 response while concurrently managing personal COVID-19 responses. Understanding pandemic-related concerns, sleep difficulties, increased substance use, and stress management strategies can promote readiness for subsequent disasters. We surveyed 3221 NG service members (75% Army; 79% enlisted; 52% 30–49 years; 81% male) during COVID-19 (August-November 2020). Almost half were activated in response to COVID-19 (mean = 18.6 weeks) and completed the survey 2–3 months post-activation. Service members indicated great concern about family health (39%), the indefinite nature of the pandemic (35%), and their financial situation (23%). Over one-third reported changes in usual sleep amount, 33% described poor sleep quality, and 21% had trouble falling/staying asleep. Increased substance use was reported by 30%, including increased alcohol (13.5%), tobacco (9%), and caffeine/energy drinks (20.1%) consumption. Chi-square analyses and analyses of variance found those who activated reported more increased tobacco and caffeine/energy drink use versus non-activated, with no sleep difficulties nor alcohol use differences. Helpful stress management strategies included spending time outdoors (53%), exercising (48%), talking to family/friends (38%), and having a daily routine (38%). Specific health-, financial-, and job-related stressors were associated with COVID-19. Incorporating stress management in planning/preventive efforts promotes resilience during disasters.