Human Systems Integration (HSI) in port/harbour security systems is directed at optimizing the performance of security personnel in identifying threats, avoiding threats, defending assets, establishing and monitoring barriers, repelling an attack, and minimizing damage. The goal of HSI in this context is to optimize performance of these personnel by providing them with efficient and effective technology, weapons, information, knowledge, decision aiding, and procedures to defeat the threat. There are challenges, however, in applying HSI to port/harbour security system design. Some challenges include: (1) designing human machine interfaces to support surveillance vigilance and situation awareness, (2) reduction of the incidence and impact of human error, (3) reduction of human workload, (4) support of decision making and provision of decision support , (5) designing displays that are intuitive and integrated, and (6) reduction of risks associated with denying access or engaging an adversary. This paper provides a rationale for the importance of considering these challenges when developing system performance requirements to be incorporated into the design and development process for the purpose of ensuring mission success.