In this study, we propose an integrated operational procedure combining a heavy-class remotely operated vehicle (ROV) with manned diving to improve the efficiency and safety of underwater search and rescue (USAR) operations in large-scale marine disasters. The procedure was developed by considering tidal-current variations and the safe operational limits of ROV, surface-supplied diving system (SSDS), and self-contained underwater breathing apparatus (SCUBA) operations. Using a spring tide window with strong current conditions, we analyzed the operational time allocation for integrated ROV–SSDS and ROV–SCUBA operations. The results showed that ROV–SSDS integration allowed a longer manned-diving window, whereas ROV–SCUBA integration required a greater proportion of pre- and post-dive ROV tasks because of the more restrictive current limit of SCUBA. In the proposed procedure, ROV-mounted sensor technologies, including sonar, depth sensors, and video systems, support situational awareness, target localization, environmental monitoring, and safety verification during integrated USAR operations. In addition, a classification framework was established by considering accident severity, support vessel requirements, manpower composition, and operational depth to support the selection of ROV-alone, manned-diving-alone, or integrated operations. These findings provide a basis for developing standardized operational guidelines for diving systems in marine disaster response.