In complex environments like harbour security, where human errors may have tragic consequences, decision support systems are essential to execute complex tasks. This paper discusses critical issues in the design of computer-based support systems that can support operators/decision-makers to better understand the situation, select a course of action, monitor the execution of operations, and evaluate the results. These aids will support decision-makers to cope with uncertainty and disorder and to help people exploit technology at critical times and places in order to ensure success in operations. Because the human cannot be completely replaced or removed from the execution of these tasks, the interaction and coordination between the human and the automated support systems become crucial. In emergency situations, that would necessitate the ability to coordinate multi-agency and multi-national operations, advanced decision support , knowledge exploitation, information fusion and management tools can significantly improve the ability to respond to such emergencies. A technological perspective alone has led system designers to propose solutions by providing operators with Decision Support Systems (DSS). These DSSs should aid the operators to achieve the appropriate Situation Awareness (SA) state for their decision-making activities, and to support the execution of the resulting actions. The lack of knowledge in cognitive engineering has, in the past, jeopardized the design of helpful computer-based aids aimed at complementing and supporting human cognitive tasks. Moreover, this lack of knowledge has, most of the time, created new trust problems in the designed tools. Providing the appropriate level of support thus requires balancing the human factor perspective with that of the system designer, and coordinating the efforts in designing a cognitively fitted system to support decision-makers.