The High Level Architecture (HLA) is a project to develop a simulation infrastructure that will promote interoperability between simulations. One important consideration of HLA development is the ability to integrate legacy systems, preferably without incurring prohibitive costs in modifying existing software. One example of a legacy system in widespread use is the US Army Simulation, Training and Instrumentation Command's Battlefield Distributed Simulation-Developmental (BDS-D) M1 Tank Simulator. The simulator is a SIMNET-based training system being used in HLA prototyping efforts. The BDS-D M1 is the only crewed human-in-the-loop simulator involved in the HLA experiments.

This paper presents research conducted by the Institute for Simulation and Training (IST) to develop a stand-alone internetworking device allowing legacy applications to be interoperable with the HLA. The Gateway provides Run Time Infrastructure (RTI) communication on behalf of the M1 simulator, in a manner that is transparent to both the M1 and the HLA participants. Of particular interest will be the intricacies of converting from HLA attribute updates to SIMNET's PDU-based updates. Also of technical interest will be the rationale for maintaining remote entity approximation (dead reckoning) models within the interface.