“O’er the ramparts we watched…” When he got to that fourth line of “The Star-Spangled Banner,” the skinny man in the tasseled shirt held the note a little bit too long, applied a little more pressure on the tremolo bar of his white Stratocaster, and sent the pitch slowly downwards, imitating the sound of an air-raid siren. America’s national anthem celebrates the heroism of the soldiers in the war of 1812. But when Jimi Hendrix performed it at Woodstock, he turned it into an outcry against the Vietnam war.