The US Navy is currently implementing "optimal manning" approaches to the design of future warships. Simply put, this emphasis takes the form of designing and deploying ships whose blend of human and mechanical/computer-based systems reduces the need for traditionally large crews while improving overall system performance and safety. Reflecting this emphasis, a Future Surface Combatant program currently in the design stage is the first Navy procurement in which the principles of user-centered design (UCD) and human-systems integration (HSI) are key design drivers. The integration of UCD and HSI methods has never been attempted in a design effort of this magnitude, and has inevitably led to illuminating insights on the part of human factors, system engineering, and other disciplines engaged in the effort. This paper provides an overview of "lessons learned," and is intended to assist the future integration of UCD and HSI principles into the design of similarly complex systems.