"This research examined the use of virtual environments as a viable dismounted infantry mission rehearsal tool. Four squads of soldiers individually conducted two missions that involved clearing a two-story building located at an urban operations training site. Two squads rehearsed the mission in a virtual representation of the exact building they would clear at the urban training site. The remaining squads rehearsed in an actual two-story building that was similar to the one they would clear at the urban training site. Squads executed both missions in each environment. Performance differences between the rehearsal groups across the two real-world' missions were small to negligible. Group performance differences for flatricides and personnel flagging were negatively affected by simulator constraints. Effectiveness ratings for the two rehearsal modes were clearly dependent on the setting where soldiers rehearsed. The research showed that while virtual environments show promise for this type of training, a number of interface and technology problems must be overcome. Currently, virtual environments do not appear to be as effective as real-world tactical training for improving skills underlying specific small unit tasks or battle drills. However, these environments may be used effectively at selected stages of training to enhance cognitive skills development."--DTIC.