Enterprise data indicates that U.S. service members (SMs) with posttraumatic stress disorder (PTSD) may not receive an evidence-based treatment (EBT) or may receive an EBT with low fidelity to the core components. Successful delivery of EBTs requires provider training and ongoing supervision/consultation, adjustment of clinic processes and structure, and leadership support. The Department of Defense (DoD) Practice-Based Implementation (PBI) Network is a dedicated team of implementation science specialists that support the integration of EBTs into clinical practice in the Military Health System (MHS). The PBI Network conducted a Cognitive Processing Therapy (CPT) pilot to investigate the acceptability and feasibility of a novel trauma specialist implementation approach proposed by South Texas Research Organizational Network Guiding Studies on Trauma and Resilience (STRONG STAR). This approach, CPT Trauma Specialist (CPT-TS), called for training designated behavioral health (BH) therapists as the primary CPT providers in their clinics. In collaboration with the Uniformed Services University Center for Deployment Psychology, the PBI Network provided training and consultation to 26 providers across 13 MHS BH clinics and supported ongoing facilitation. Despite provider interest and clinic leadership support, less than half of the pilot provider participants were able to meet the consultation and CPT delivery requirements for designation as a CPT trauma trained specialist. Prevalent implementation barriers included lack of adequate clinic resources, provider challenges balancing clinical and military-related duties, the need to focus on high-risk patients, and other military system-related constraints. These findings highlight the need for implementation scientists to examine alternatives to traditional training models and identify fidelity-consistent adaptations that allow for delivery of evidence-based care within highly constrained systems of care. Impact StatementThis article presents the evaluation of a pilot implementation of evidence-based psychotherapy for the treatment of posttraumatic stress disorder (PTSD) in the Military Health System (MHS). A team of implementation science specialists trained interested outpatient behavioral health (BH) providers as Cognitive Processing Therapy trauma specialists in their clinics. Multiple patient and system-level factors challenged the delivery of this evidence-based PTSD treatment. The results emphasize that rollout methods established in one health care system may not translate well to another and provide actionable information about the delivery of evidence-based psychotherapies within the MHS and strategies to improve the quality of BH delivered to U.S. service members.