DARWARS Ambush! is a multi-player, game-based training system for convoy operations, developed for DARPA in 2004 and currently in use by our warfighters at numerous bases in the U.S. and abroad. It was designed originally to reinforce the practical skills and TTPs (tactics, techniques and procedures) needed to anticipate and react to convoy ambushes and improvised explosive devices. However, its users have extended its application to address leadership skills, rules of engagement, dismounted urban operations, and many types of missions. We will describe the factors we see having led to the widespread grass-roots adoption of DARWARS Ambush! and the implications for developing and deploying other game-based training systems. We will also discuss the innovations—both in content and application—made by the Ambush! user community, and reported on at the recent Ambush! Users Conference. This example of adoption and innovation by the user community, with minimal contractor assistance, illustrates the value of putting training content creation into the hands of people close to the action, and that the ability for users to control and adapt content themselves leads to an effective, flexible training environment.