In this paper, a cloud-based mission control architecture is proposed to achieve flexible remote access and coordinated mission control among a fleet of unmanned surface vehicles (USVs). First, a cloud-based mission control architecture that renders easy, timely and prioritized remote access to the USVs regardless of the remote operator’s location is proposed. It is achieved by leveraging remote cloud-based technology and local Operating onboard System. Decentralized property of the architecture accomplishes scalable monitoring, remote control, data acquisition and missions sharing for an USV fleet. Second, the related software interfaces are required for this task: the user interface of the remote client that is used for mission control/planning and data visualization and that is applicable across mobile robotic systems; and the back-end interface for the local USVs that bridges robotic and cloud server and provides seamless integration with the well-established Robot Operating System (ROS). ROS is nowadays, the most widely used framework for robotics developments. Furthermore, the proposed cloud-based mission control architecture is implemented on a fleet of real vehicles, H2Omni-X USVs, and the performance of the remote experimentation is demonstrated during sea trials at the Adriatic coast, Croatia, representing the practical contribution of this paper.