The (Simulation Based Acquisition) SBA process is one in which the planning, design, and test of a weapon system or other product is done through the more effective use of modeling and simulation, information technology, and process improvement. This process results in a product that is produced faster, cheaper, and more reliably than its predecessors. Because the SBA process requires realistic and detailed simulation conditions, it was necessary to develop a simulation tool that would provide a simulation environment acceptable for doing SBA analysis. The Joint Integrated Mission Model (JIMM) was created to help define and meet the analysis, test and evaluation, and training requirements of a Department of Defense program utilizing SBA. Through its generic nature of representing simulation entities, its data analysis capability, and its robust configuration management process, JIMM can be used to support a wide range of simulation applications as both a constructive and a virtual simulation tool. JIMM is a Mission Level Model (MLM). A MLM is capable of evaluating the effectiveness and survivability of a composite force of air and space systems executing operational objectives in a specific scenario against an integrated air and space defense system. Because MLMs are useful for assessing a system's performance in a realistic, integrated, threat environment, they are key to implementing the SBA process. JIMM is a merger of the capabilities of one legacy model, the Suppressor MLM, into another, the Simulated Warfare Environment Generator (SWEG) MLM. By creating a more capable MLM, JIMM will not only be a tool to support the SBA initiative, but could also provide the framework for the next generation of MLMs.