This paper reports on development of a Web-based capability for distributed simulation in large-scale virtual environments that has been developed collaboratively by the Naval Postgraduate School and George Mason University. The work brings together several years of effort in DIS-Java-VRML and the Virtual Reality Transfer Protocol on the part of NPS with a similar period of effort by GMU in Selectively Reliable Multicast for distributed virtual simulation combined with Java-based middleware for use with the DoD High Level Architecture (HLA) for modeling and simulation. We describe the capability we have created for simulations of military and other highly interactive, physics-based models to operate in three-dimensional visualization over advanced Internet facilities. The major components of our system are described in detail, with the intent of creating interest in their use by the academic community.