When on May 15, 1918 a French lieutenant warned Henry Johnson of the 369th to move back because of a possible enemy raid, Johnson reportedly replied: "I'm an American, and I never retreat." The story, even if apocryphal, captures the mythic status of the Harlem Rattlers, the African-American combat unit that grew out of the 15th New York National Guard, who were said to have never lost a man to capture or a foot of ground that had been taken. It also,...