The annual Robotic Experimentation and Prototyping with Maritime Unmanned Systems (REPMUS) Exercise is one of the world’s largest testing events for maritime robotics and uncrewed systems. 2025 marked the 15th edition of REPMUS, and for the first time, was conducted jointly with NATO’s Dynamic Messenger (DYMS) exercise, which is part of NATO’s Operational Experimentation (OPEX) series. The joint event provided opportunities to test and evaluate emerging technologies in a realistic and operational environment while supporting NATO’s goal of maintaining a technological and tactical edge.