This study evaluated trends in the prevalence of overweight, obesity, and diabetes among active component service members between 2018 and 2021, before and after the start of the COVID-19 pandemic. This study also investigated the incidence of prediabetes and type 2 diabetes mellitus (T2DM) diagnoses during the same period. Between 2018 and 2021, the prevalence of obesity among active component service members who completed a Periodic Health Assessment (PHA) increased from 16.1% to 18.8%. The incidence of prediabetes increased from 588.2 to 763.8 cases per 100,000 person-years (p-yrs), and the incidence of T2DM increased from 55.5 to 69.6 per 100,000 p-yrs. The largest relative increases in obesity prevalence were in the youngest (<30 years) age categories. Navy members and Hispanic service members experienced the largest absolute and relative increases in rates of new diabetes diagnoses. These findings indicate that during the COVID-19 pandemic active component service members experienced increased prevalence of obesity, prediabetes, and diabetes. Evaluation of lifestyle factors associated with these chronic diseases among service members may be useful to enhance deployment readiness and operational effectiveness.