DOD, the United States Department of Defense.

DOD "is the U.S. federal department allocated the largest level of budgetary resources and charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the United States armed forces. The Department of Defense is an evolution of the Department of War." 

The DoD is the major tenant of The Pentagon building near Washington, D.C., and has three main components—the Departments of the Army, Navy, and Air Force. 

- Excerpted from http://en.wikipedia.org/wiki/United_States_Department_of_Defense