Conducting robust, reoccurring Joint CAS training for Terminal Attack Controllers (JTACs) on live ranges is problematic. While stationary observation points and targets are useful for initial and basic call for fire training, live bombing ranges do not provide mobile, realistic targets for training in troops in contact, joint/coalition training, and operations in urban terrain. Distributed simulation and Live-Virtual-Constructive networks can provide JTACS with training to enhance their team, inter-team, and joint skills with greater frequency, at lower cost, and potentially more combat realism than live-range training exercises. One of the key advantages of distributed simulation training for JTACs working with attack aircraft, is that the activities can be focused on specific skills such preparing and communicating 9-line coordination briefings, procedurally "talking aircraft on to" targets, and coordinating for directives, priorities and deconfliction of fires. Fidelity requirements for computer generated forces (CGFs) have typically revolved around air-to-air fighter training or large scale wargaming. In 2004, the Air Force Research Laboratory initiated a Joint Terminal Attack Control Training and Rehearsal System research and development project. The goal of this effort was enhancing JTAC readiness by designing, developing and evaluating an immersive, DMO compatible training system using fully integrated JTAC equipment. After initial system evaluations by JTAC subject matter experts, it was apparent that the CGF scripting, intelligent behavior, systems models, and weapons would need major modifications to support effective JCAS training. To overcome these difficulties researchers developed a rapidly customizable CGF environment and instructor operator station. This paper discusses some of the unique modifications made to CGFs to support JTAC training and overall lessons learned from modeling and simulation of the JTAC environment to include behavior scripting, artillery models, realistic air-to-ground weapons delivery simulation, modeling the air-to-ground C2 environment, instructor tools, and scenario management.