This 25-page report, published by the Chinese Manufacturers' Association of Hong Kong Secondary School, describes the design and construction of an underwater remotely operated vehicle (ROV). This report was created by CMA Underwater Expert Limited, a student group that participated in the 2021 MATE ROV competitions Ranger class. MATE ROV is a global underwater robotics competition for STEM students. The competition includes Explorer, Ranger, Navigator, and Scout classes.In the report, an abstract introduces the project and group. The design rationale is then presented, which includes information on the ROV's aim, design process, design philosophy, tether, frame, electrical distribution control panel, VEX...