This paper describes a simple distributed simulation for support of emergency response exercises. The simulation, called the Immersive Synthetic Environment for Exercises (ISEE), was inspired by the simplicity of web-based role playing games (RPGs) which have all the elements of distributed simulations, but do not rely on complex interoperability software or high-end graphics engines. ISEE uses PHP to generate user interfaces, MySQL as simulation middleware, and agent-based simulations written in Python determine the behavior and state of simulated objects. It uses a web-interface that allows players to see events, communicate, and assign resources to critical emergency response functions. Test showed that up to 1000 entities could be represented with a quarter second simulation time step. The application was deployed as a prototype to support a masscasualty emergency response exercises in May of 2005. Results of the exercise showed that the intended value of distributed simulation (multi-user, immersive experience) was achieved using simple tools with a rapid development time.