This article describes an autonomous guided vehicle (AGV) system designed to transport ISO standard cargo containers in port environments. The AGV consists of a large 17.5-ton chassis, which is driven and steered through a diesel-hydraulic power set. The vehicle drives on pneumatic wheels over unprepared road surfaces at speeds up to 6 m/s. The navigation system is based on the use of millimeter-wave radar sensors detecting beacons placed at known locations in the environment. The navigation system reliably achieves accuracies of better than 3 cm. The planning and control systems allow the AGV to operate in the quay and yard area, to dock with gantry cranes, and to achieve a duty cycle comparable to that of a conventional manned vehicle. This article concentrates on describing three principal contributions of this work: the design of the overall vehicle and on-board systems architecture; the development of a navigation system appropriate for large, outdoor, high-speed vehicles; and the experimental program leading to validation of the vehicle system.