On June 17, 1940, just after the Dunkirk evacuation had supposedly ended in success, several thousand of the many British troops still left in France boarded a five-decked cruise liner called the Lancastria. Right after they boarded, the ship was dive-bombed by the German Luftwaffe, and a short time later the 17,000-ton Lancastria sank. German fighter planes strafed the oil slick sea, setting it ablaze as British troops banded together singing "Roll...