TNO Defence, Security & Safety has a long history of applied research in the area of automated simulator-based training by means of Computer-Assisted Instruction (CAI). Traditionally, a CAI system does not enable a true dialogue between the learner and the virtual instructor. Most frequently, the system acts like a human expert, and authoritatively provides feedback and ways to improve the task performance. In this paper, we describe an educational agent that enables a dialogue between the learner and the agent. The agent is called the companion agent. It acts like a virtual co-learner, for example by deliberating about new operational measures after a situation-change. The agent operates on the same authority level as the learner, and is therefore less threatening than a traditional virtual instructor. We believe companion agents are typically useful in modern, constructive learning situations where learners can take control of their own learning process. Potential applications of companion agents lie within the civil area (for example a civil tunnel operator during tunnel surveillance training) and the military area (for example embedded training in tactical surveillance).