ABSTRACT Service members transitioning to civilian life have suicide rates that are 63% higher than other service members, and rates are especially high in the first year after separation from service. Therefore, the President issued an Executive Order that requires the Department of Veteran Affairs (VA) to develop a plan to provide, suicide prevention resources to transitioning service members in the year following separation from service. In response, VA’s Central Office Suicide Prevention Program (SPP) plans to implement a Caring Letters campaign for all 245,000 service members who transition each year. In the Caring Letters intervention, a series of messages are sent to individuals to communicate that they are not forgotten, and that people care about them and are concerned for their well-being. The messages also serve as a reminder that help is available. Multiple randomized clinical trials support the efficacy of Caring Letters for reducing suicide and suicide attempt rates. The Joint Commission has recently promoted Caring Letters. The campaign for transitioning service members faces some unique challenges, however, since there is no established VA provider to serve as the signatory. Therefore, we propose a partnered program evaluation between SPP and the proposed evaluation team to examine the use of Caring Letters in this new population. Specifically, the evaluation will test two models: (1) A modified approach to Caring Letters in which letters are sent from a VA provider the Veteran does not know, and (2) a culturally-sensitive peer-based approach to Caring Letters in which letters are sent from recently transitioned service members matched on sex and military service branch. The campaign will also randomize service members to a standard mailing schedule (8 messages in a year) or a high frequency schedule (14 messages in a year). In Aim 1, we will evaluate the effects of Caring Letters on clinical outcomes and VA clinical utilization rates. In Aim 2, we will examine the effects of the two different Caring Letter signatories and two different mailing schedules on the clinical effectiveness of the intervention. Aim 3 will examine facilitators and barriers to implementing the Caring Letters campaign. In Aim 4, we will conduct budget impact analyses of implementation from the VA perspective. This will be the largest evaluation of a Caring Letters intervention ever conducted, and it will provide direct and actionable data to leadership to evaluate the impacts of this major prevention campaign.