PROJECT ABSTRACT Weight gain is disproportionately high among young adults (YAs) with average weight gain of 30 lbs. occurring between ages 18-35 and is associated with an early worsening of CVD risk factors. Primary prevention of weight gain is important because weight loss is difficult to achieve, access to programs is limited, and initially successful people regain weight over time. Weight gain is a serious problem in the Department of Defense, our nation’s largest employer, with more employees than Walmart or Amazon. The military, comprised largely of YAs, has growing rates of obesity and yearly weight gain. Many people believe that young, active-duty men and women are fit, lean, and healthy because of the military lifestyle and protected from obesity. Unfortunately, obesity rates in active U.S. military personnel have mirrored those of civilians. Furthermore, inability to maintain a healthy weight results in early discharges and threatens the readiness of well-trained Airmen to be deployed. Overweight in the military is now considered a threat to national security. Few weight gain prevention (WGP) trials have been done in military populations, and previous trials with YAs have mixed results and poor external validity. Our proposal is designed to address the major public health problem of weight gain in the military, as well as address notable gaps in pragmatic mHealth and WGP trials. The SNAP- M intervention will be adapted, with partners and key stakeholder from the US Air Force, from our evidence- based WGP intervention for YAs, the Study of Novel Approaches to weight gain Prevention (SNAP). SNAP tested 2 self-regulatory interventions in 599 general population YAs and found that both reduced weight gain over 2-3 years compared to controls. This project proposes to make 1) critical adaptions to SNAP to facilitate translation and 2) conduct a Pragmatic Hybrid Type 1 Effectiveness Trial of the SNAP-M intervention using a 2-group randomized controlled trial (RCT) design in 454 Air Force Airmen recruited from 4 military installations with the primary outcome of mean weight change from baseline to 2 years. We will compare the groups on key outcomes and examine potential moderators of treatment effect. Additionally, we will apply a RE-AIM Framework to determine reach and representativeness, and potential for organizational-level adoption, implementation, and maintenance of SNAP-M, if successful. The proposed research fills key research gaps in an underserved population in critical need of weight gain prevention with completely remote delivery suitable for YAs in the military.