We discuss the practical issues in modeling federation architectures in the case of Naval Surface Tactical Maneuvering Simulation System (NSTMSS), an HLA-based distributed interactive simulation system. We model the architecture of NSTMSS conforming to the Federation Architecture Metamodel (FAMM). FAMM provides a formalized language to specify the communication behaviors of federates along with their object models. Federate behavior specification is based on Live Sequence Charts. A federation architecture model conforming to FAMM is amenable to automated processing. In particular, it serves as a source for federate application base code generation.