In 1992 we began the development of a ground vehicle simulation software architecture that was specifically designed for evolvability. This architecture along with its supporting development processes and standards was reused throughout the 1990's on a variety of Army programs. We have now taken this software architecture, which was designed for stationary simulation in crewstations in a laboratory environment and reused it to add embedded simulation capabilities to fielded ground vehicles. The purpose of embedded simulation is to enhance soldier effectiveness both before and during actual battlefield conditions. As a result, in a fielded ground vehicle, the computer specialist responsible for setting up, starting, controlling, monitoring and stopping the simulation is not present. Unlike in a laboratory environment, in a fielded vehicle the simulation software itself is responsible for performing these functions. This paper describes how our simulation facility software architecture has been adapted so that it could be reused for embedded simulation. We thus provide a case study illustrating characteristics of a system architecture that allow it to be long-lived by evolving not only to changing requirements due to technological and methodological changes but also changes due to new and previously unthought-of patterns of system utilization. We also share what we have learned about the development of embedded software systems that need to be able to run without human operator intervention.