March 4 is the only day on the calendar that’s also a military command — march forth! — so it’s only appropriate that this be the day that we celebrate the servicemen and servicewomen in our lives with National G.I. Day. Soldiers in the U.S. military — including members of the Army, Air Forces, and Marines — have been referred to as G.I.s since 1940, and today is the day that we celebrate everything they do for us with a big hug, either literal or metaphorical.