The One Semi-Automated Force (OneSAF) program is being developed to replace a number of models and simulations currently used in the training domain as well as those used for analytical purposes. With the Operational Requirements Documents requiring both human in the loop and closed form, stand alone and distributed modes of operation, and support to a myriad of users, a single monolithic simulation could not satisfy the variations in expected uses. Use of an innovative product line architecture which allows the user to compose a particular instantiation of the simulation for each use case from a hand basket of tools, will enable OneSAF to meet it's widely varying user needs. The product line architecture will also be designed for constant replacement or modification of tools and modules as dictated by the evolving tactical operational requirement. The paper details the breadth of the requirements, and differing operational architectures, and how the architecture is designed to be instantiated from multiple tools and models, by the user, at runtime.