There are many important maritime facilities and ships including petroleum tankers operating along the Japanese coasts that could become the targets of terrorism. In addition, Japan has been suffering from continual crimes such as illegal dumping and smuggling in the water spaces. For the purpose of preventing terrorism and regulating underwater crimes, we have conducted a 3-years study, begun in 2005, entitled "Development of an Underwater Security Sonar System", based on which an integrated underwater monitoring system has been realized, with the support of the Special Coordination Funds for the Promotion of Science and Technology of MEXT. In this paper, bearing practical implementation of this system in the actual monitored sea areas in mind, optimum methods of underwater acoustic image monitoring are considered. Furthermore, to develop a more effective monitoring system, we explored monitoring techniques that involve putting together information from infrared cameras, marine radars or AIS, and tried to develop a complex display monitoring technique in which the sonar images are simultaneously projected together with map information. We confirmed the effectiveness of this system through various operational tests and demonstration experiments in the actual sea area.