In this paper we describe a multi-agent simulation called the Human Agent Virtual Environment (or HAVE). HAVE is a test bed to explore agent-environment interaction in multiagent simulation for defence applications. The primary research driver in the development of HAVE is to explore representations of virtual environments in which both humans and agents are situated, perceive these environments and undertake meaningful and appropriate actions. HAVE models and simulates a Close Air Support (CAS) mission which involves fighter or strike aircraft providing support to ground troops through the use of air-to-ground weapons.This provides a realistic and currently extremely relevant domain in which to explore agent-environment interactions. Three important research challenges have been addressed by the work. The first, is the implementation of a multi-modal representation of the virtual environment, having multiple, parallel yet consistent representations of the virtual world that were accessible to, and tailored for the different simulation components. The second is the used of labeled annotations in the virtual world which the agents could easily access and interpret. The third, the use of an appropriate architecture for capturing and representing interaction between agents and the environment they are situated in.