Effective ballistic missile defense (BMD) training requires a highly distributed integrated training environment that stimulates deployed forces throughout all elements of the BMD System (BMDS) including sensors, launchers, and command and control systems manned by US, NATO, and Coalition forces. This paper will describe BMD FST at Sea development and assess its effectiveness in supporting distributed BMD training using test data and lessons learned during at-sea exercises. A significant challenge in building this distributed environment is stimulating deployed maritime BMD assets that provide early detection and engagement of ballistic threats. Current at-sea training capabilities are restricted to onboard training systems that cannot share simulation data between ships because shipboard satellite communication networks have relatively limited bandwidth, high latency, and are not connected to land-based simulation networks. The Navy Warfare Development Command (NWDC) has developed a cost-effective solution to stimulate live Aegis BMD shipboard training systems at sea with virtual and constructive models by integrating the Navy Continuous Training Environment (NCTE) using shipboard satellite communication networks. NWDC has deployed and exercised this new capability using a variety of complex integrated air and missile defense (IAMD) scenarios to test whether ships can conduct detection and engagement of ballistic missile threats shared simultaneously with other BMDS training systems, while participating in coordinated command and control between BMDS elements and the Combatant Commander. NWDC has demonstrated this capability in several at-sea training exercises, leveraging the NCTE's connection to other distributed training networks from Missile Defense Agency, including in-theater BMDS elements such as Patriot, THAAD, and TPY-2. Using this capability, Combatant Commanders will conduct more realistic training exercises that support mission rehearsal, are scalable to all levels of command and control, and can facilitate experimentation for development of new and more robust Tactics, Techniques, and Procedures, while allowing BMD ships to remain deployed at sea.