This paper details the design concept and process of an application-specific case rule-based reasoning engine (CRBRE) for double-agent convoying, although it has a frame that has generality. The design was accomplished using the plan, design, check and change (PDCC) design cycle. The engine has a 3-cycle configuration of perception step from agents, environment and their interaction; action step to them; and transform step from perception to action (PTA-cycle). Many applications such as multi-agent and multi-object systems with triggers will be possible to achieve.