I was struck by the traditional parts of the D-Day ceremonies today, the 65th Anniversary of the invasion of Normandy--the 21 gun salute, the playing of Taps, and the missing man flyover. Because I was interested in the origins of these traditions, I thought you might be, too.
What Does D-Day Mean? From the National D-Day Memorial Foundation.
The 21 Gun Salute: Discharging an early cannon rendered it ineffective; thus, firing the cannon in a ceremonial fashion shows peaceful intent, and today is the highest honor rendered by a nation. For the entire history and origin of this ceremony, see the U.S. Army Center of Military History's Origin of the 21-Gun Salute.
The playing of Taps--you can read an explanation of the origin and the words, which I remember singing as a Girl Scout, from The West Point Connection: 24 Notes That Tap Deep Emotions, by Jari A. Villanueva.
The "Missing Man" Flyover--this is extremely dramatic and touching to watch. Four planes approach in formation and one splits off, often flying off into the sunset, to represent those who died in action. For a complete and detailed description, see the Wikipedia entry, Missing Man Formation.
Here is a video demonstrating one version of the flyover, as performed at the Great Georgia Air Show in 2006.