We describe our continuing work on the development and use of collaborative virtual environments (CVEs) in support of mission rehearsal activities for the very shallow water mine countermeasures mission. These multi-participant CVE's are built from multiple data streams that include archived circulation model results, 3D model files, moving entities and observations from advanced instrumentation. A room-sized projection screen device called the CAVETM is used to visualize and interact with the CVE, although single walled devices and workstations may also be used. Asynchronous collaborative capability allows users at many distributed sites to partake in a many-to-many session that takes place in a common virtual world. Incorporating multiple data streams, these CVEs allow multiple users to view, navigate, and interact with data in a 3D environment, including graphical representation of bathymetry/topography, above- surface images, in-water objects (e.g. mines, bridges), and hydrographic characteristics (e.g. currents, water levels, temperature).