Sandia Labs gave a presentation about using commercial game engine technology for the purposes of developing adaptive thinking and leadership skills. http://www.cmpevents.com/GDsg05/a.asp?option=G&V=3&id=272352 An interesting quality of this similation is the focus on inter-cultural communication, how to make decisions in high-stress/uncertain conditions, and learning/adapting to situations over time - this is not a "tactical trainer" in the traditional sense.
Their solution was adapted from America's Army which is based on the Unreal2 engine. See: http://www.sandia.gov/news-center/news-releases/2005/def-nonprolif-sec/americaarmy.html This was a joint effort between Sandi and the U.S. Army's JFK Special Warfare School. Simulation can be used by individuals or in a team learning environment.