It was on this day in 1775, that the Continental Congress approved a resolution to form the Continental Marines ... and the rest, as they say, is history.
Two battalions of Marines were raised to conduct ship-to-ship fighting, provide shipboard security and assist in landing forces. With their maritime mission in mind, recruitment was held on Philadelphia's bustling waterfront, at Tun Tavern ... some might say an appropriate place to find Marines!
The birthday of the Corps is celebrated worldwide, wherever Marines are posted. It was a big night in our household, with my parents in formal dress, heading out to spend the evening at the Marine Corps Ball.
Here is Wikipedia's write-up on Marine Corps history, a brief write-up about that first recruitment on the official USMC site, and a page devoted to this year's Commandant's Marine Corps Birthday Ball.