The Army has not assessed the effectiveness of the Triad of Care model, the core structure of the Warrior Transition Unit (WTU) program, consisting of a team of three key staff that provide medical case management. The Army established the Triad of Care model at a time when WTU soldiers' diagnoses were primarily for physical conditions. Since then, the composition of diagnoses has changed significantly. Specifically, in 2008, about 36 percent of the 12,228 soldiers who entered the WTUs had a behavioral health diagnosis. In 2015, however, over half of the 2,628 soldiers who entered the WTUs, about 52 percent, had such a diagnosis. Despite the change in the composition of diagnoses, the Army has not assessed its approach for managing soldiers' care. Officials from the five WTUs that GAO visited stated that they have added social workers to the Triad as an ad-hoc measure to provide better case management and certain types of behavioral health services. These local adaptations represent efforts to meet an immediate medical need and support the need for analysis of whether the Triad model should change. Assessing the Triad in light of the changes in WTU soldiers' diagnoses would position the Army to better determine how to meet WTU soldiers' medical needs. The Army faces challenges in its oversight of the selection of squad leaders and platoon sergeants to staff WTUs, in the evaluation of staff training, and in the ability to adjust future staff levels if needed. Specifically, the Army has established selection processes and updated its selection criteria for these WTU personnel, but it is not exercising oversight responsibility to track full adherence to these policies, specifically the Army's requirement to interview candidates for these positions. Candidates for these positions are drawn from a mix of Army occupations, and the selection process, including interviews, is intended to ensure the suitability of the staff selected for these sensitive positions. While the Army has taken steps to improve its training program for squad leaders and platoon sergeants, the program does not incorporate a post-training assessment of the application of training to the work environment. Without information that could be obtained from such assessments, the Army may miss an opportunity to incorporate information concerning the practical application of training. In addition, the Army has not developed plans for how it would increase WTU staff levels, if needed, to support any potential future increase in demand. The ability to reverse the decision to inactivate 11 WTUs by August 2016 was a key planning consideration for the Army. However, without a plan to address staff level changes, the Army lacks assurance that it can select, train, and assign staff to its WTUs in a timely manner. While the Army has implemented a process for reviewing the eligibility of soldiers to be admitted to WTUs, it does not track instances in which Commanders have made exceptions to these criteria. By not tracking this information, the Army does not know how frequently such exceptions are made and cannot ensure the best use of resources. In addition, the Army is planning to expand a WTU-alternative program to the Army Reserve, but has not examined the costs and benefits of such an expansion. Without comparing the costs and benefits of program expansion with the current system, the Army could incur significant costs without clearly articulated benefits.