Contact the Department of Defense by calling (703) 571-3343 as of 2015. The main location of the DoD is 1400 Defense Pentagon, Washington, D.C. 20301-1400.
Another way to contact the Department of Defense is by visiting the official U.S. Department of Defense website. The top drop-down menu offers a contact option. This leads to a full page of contact information depending on the query.
In the United States, the DoD is the largest and oldest government organization. Its duty is to address potential war concerns and protect the country by supplying military forces. After the War Department was created in 1789, the Department of Defense followed.