The Joint Semi-Automated Forces (JSAF) simulation is a large program that has been modified across many developers. A complete and concise software architecture map of it has not previously existed. Such a map would assist new developers in understanding JSAF and speed development by allowing developers to quickly see relationships without having to conduct time-consuming searches of the documentation of several libraries. It also supports design of efficient regression tests of modifications by highlighting specific interactions that needed to be tested. JSAF was reversed engineered and organized with the assistance of software tools into a model. Requirements were then entered into the model and graphically traced down to the software. This end result provides a clear, graphical picture of the JSAF architecture. In addition to the benefits previously stated, this model helps document the connection between the software and requirements. This paper details the process of reverse engineering JSAF and the advantages of using a software model to implement development.