Oh boy, here goes the U.S. Army educating the U.S. Marines, again...
"While the U.S. Marine Corps is a separate and distinct service branch, it has many close ties to the U.S. Navy, and the Department of the Navy oversees both service branches, each having its own autonomous leadership."
U.S. Army birthday: June 1775
U.S. Marine Corps birthday: November 1775 - beat you by 5 months.
Yeah, I can do without the beret, lousy headgear. But hey, the U.S. Air Force wears berets, the British SAS wears berets, and the French Foreign Legion wears berets. The U.S. Army has always imitated the British.