The National Museum of the United States Army in Fort Belvoir, Virginia, is a wonderfully educational experience following the history of the United States Army from 1775 to present. The exhibits are very interesting and set up in a logical manner.
Although the other military services are not represented here, it is a very comprehensive history of the United States Army. Admission is free and it is a great way to spend a day if you are in the Fort Belvoir, Virginia area. It will take at least the better part of a day to see most of the exhibits and they do have a cafeteria on site.
National Museum of the United States Army
1775 Liberty Dr.
Fort Belvoir, VA 22060