The Joint Terminal Attack Controller (JTAC) warfighter is responsible for supporting the Army Maneuver commanders by controlling aircraft and weapons employment in Close Air Support (CAS) environments. JTACs are typically co-located with Army units, however, they are required to communicate and collaborate with a number of personnel operating external to their locations. JTACs are required to maintain a significant level of proficiency by regularly training in both live and simulation environments. Due to increasing reductions of aircraft to aide in live training events and limitations in simulator technology, trainings gaps have arisen that hinder the opportunities for JTACs to achieve required levels of proficiency. This paper will introduce an ongoing effort to create a robust JTAC training environment ‒ the Joint Terminal Attack Controller-Training Rehearsal System (JTAC-TRS). The JTAC training gaps are being assessed and explored within the JTAC-TRS using problem-based learning approaches by analyzing the Mission Essential CompetenciesSM (MEC). Using MECs, we have identified the primary and supporting competencies, knowledge, skills, and developmental experiences that a JTAC must have to effectively execute the mission. Preliminary evaluations of this system demonstrate that the JTAC-TRS has reduced 50% of these training gaps. We will present data regarding the identified training gaps and how they are addressed in this unique training environment.