The CACTUS project was concerned with command and control training of large incidents where public order may be at risk, such as large demonstrations and marches. The training requirements and objectives of the project are first summarized justifying the use of knowledge-based computer methods to support and extend conventional training techniques. The software designs are based on a world model in which crowd groups and police units are placed on a digitized map and have probabilistic rules that govern their interactive behaviour. The simulation runs as a decision-making exercise that can include pre-event logistic planning, incident management, and debriefing evaluation. A key feature is the flexibility of the software, for it provides not only a working simulation but also a methodology and software tools for customizing programs to suit particular circumstances and training needs. [The case study was first published in "Interactive Learning International," Vol. 8, no. 2, 1992, 127-136, by John Wiley & Sons Ltd. (EJ446123).]