That's the total number of military veterans in the United States as of 2011, according to the U.S. Census Bureau, in a fact sheet aboutVeterans Day 2012, which contains many other interesting statistics about Those Who Served.
Of the 21.5 million U.S. veterans, 1.6 million are women.
9.2 million are older than 65; 1.8 million are younger than 35.
3.5 million veterans have a service-connected disability rating.
For more hard numbers, the VA's National Center for Veterans Analysis and Statistics has a motherlode of information about the veteran population.
And...just in time for Veterans Day, a new feature on the Arlington National Cemetery website: ANC Explorer.
Arlington National Cemetery has developed ANC Explorer, an application that is available across common web browsers and on mobile smart phones. This app enables veterans, family members and the public to explore Arlington's rich history.
This first version of ANC Explorer allows users to locate gravesites, events,or other points of interest; generate front and back photos of a headstone or monument; and receive directions to those locations.
In the future, ANC Explorer will offer features such as emergency and event notifications,restroom and water fountain locations, shuttle stops and self-guided tours.
Kiosks for accessing the ANC Explorer are available for public use in the Visitor Center and in several locations throughout the cemetery.