In late 2008, DISA (Defense Information Systems Agency), the global IT arm of the US Department of Defense, embarked upon a project to create an internal collaboration and software application lifecycle management system. Beyond simply fielding yet another tool, the Forge.mil effort was designed to fundamentally change the way the DoD developed and acquired software technology and systems. The method of this change was the application of Open Source principles inside of the larger DoD community, including ideas such as meritocracy and code sharing, as well as Agile and collaborative software development. This lightning talk will explain the rationale behind Forge.mil, how it was developed using Open Source principles, and how it continues to influence technology acquisition within the DoD in both practice and policy changes.