A distributed, parallel implementation of the widely used Modular Semi-Automated Forces ModSAF Distributed Interactive Simulation DIS is presented, with Scalable Parallel Processors SPPs used to simulate more than 50,000 individual vehicles. The singleSPP code is portable and has been used on a variety of di erent SPP architectures for simulations with up to 15,000 vehicles. A general metacomputing framework for DIS on multiple SPPs is discussed and results are presented for an initial system using explicit Gateway processes to manage communications among the SPPs. These 50K-vehicle simulations utilized 1,904 processors at six sites across seven time zones, including platforms from three manufacturers. Ongoing activities to both simplify and enhance the metacomputing system using Globus are described. 1 The Large-Scale DIS Problem Over the past few years, Distributed Interactive Simulation DIS 1 has become an increasingly essential tool for training, system acquisition, test and evalu...