The increase in the number and tonnage of modern vessels, the large differences in their handling qualities, the dimensions of straits and ports, and consequently navigation difficulties encountered in poor visibility, have led the authorities involved to set up control centres responsible for the functions of traffic regulation and aids to navigation. Several systems ensuring these functions have been set up over the last few years or are currently under way. Using modern technology these systems meet a wide range of operational requirements and are characterized by extensive modularity, allowing system implementation in successive stages.