Abstract : MDT2 Lessons Learned Final Report on the Close Air Support exercises completed over a long-haul classified network. The Battlefield Distributed Simulation - Developmental (BDS-D) simulation program has demonstrated that man- in-the-loop distributed interactive simulation systems, including an active, intelligent opposing force, can explore the validity of planned hardware configurations as well as the concepts for employment, doctrine, and tactics. The objective of the Multi-service Distributed Training Testbed (MDT2) Training Exercise was to demonstrate the capability to conduct meaningful multi-service, combat mission training using Distributed Interactive Simulation (DIS) technologies and synthetic battlefields. The focus for this training demonstration was close air support (CAS). The Multi-Service Distributed Training Testbed linked simulations and simulators of all four Services classified at a SECRET/NOFORN level. Airframe crew simulators of Air Force pilots at Armstrong Labs, Mesa, AZ (formerly Williams AFB, AZ), and Marine and Navy pilots at Systems Engineering Test Directorate, Patuxent River, MD, emulated attack and forward air control aircraft. They supported the conduct of ground force operations by Army elements in Advanced Distributed Simulation vehicles and Tactical Operations Center (TOC) at the Mounted Warfare Test Bed (MWTB), Fort Knox, KY. Additionally, a Marine Deployable Forward Observer (DFO)- MULE (ground laser designator) team participated from NRaD-San Diego, CA, using their target identification simulators. The key to the demonstration were the performance measurement and feedback systems used for the CAS training.