Creating all components from scratch is impractical for the joint synthetic battlespace (JSB) due to the huge scope that JSB needs to cover. Spanning training, acquisition, test and evaluation, and research and development, JSB supports the DoD from the detailed engineering level, entity level, mission level, to the operational and strategic levels, while supporting community users. Thus, the JSB must leverage all existing investments to the fullest extent possible. It is expected that existing simulations cannot cover some of the JSB space even though all the existing components are fully integrated under the JSB infrastructure. The missing pieces will need to be created to achieve the goal and vision of the JSB. The JSB will therefore be a combination of legacy simulations and the newly created JSB components in future. We discuss the JSB component integration framework that facilitates integration of the existing legacy simulation systems as well as one of the new JSB components, the JSB common synthetic environment (JSB CSE). It also presents the on-going high performance computing (HPC) applications of the JSB as its computing infrastructure.