You know the song, but let's hear it anyway given the news of the day. More, let's hear it a cappella since their brothers apparently didn't need instruments to perform.
UPDATE: Apparently the initial reports were wrong: no Marines were involved. The three Americans were a National Guardsman, an Airman, and a civilian. A Briton and one Frenchman were also involved in taking down the attacker. You can read about them here.
Strong work, gentlemen.