March 15, 2011
March 15 is the designated birthday of The American Legion. On that date in 1919, the first American Legion caucus, held by members of the American Expeditionary Force, convened in Paris. Much as the birthday of the United States is celebrated on July 4 - for the date in 1776 when patriots declared the independence of the British colonies and the spirit of America was born - March 15 is the date when The American Legion came to life.
Go to http://www.legion.org/library/8737/preparing-celebration for a story on how various posts celebrated last year's birthday, and how your post can celebrate this year's.