More than half of the U.S.’s aircraft losses in Europe in World War II were due to German antiaircraft artillery, and many of the American aircraft shot down by Luftwaffe fighters had first been driven out of formation by flak and made easy prey for the fighters. A world away in the Pacific, American flak guns aboard naval ships formed the last line of defense against Japanese kamikazes. Historian Donald Nijboer relies on firsthand accounts, newly discovered files, photos, diagrams, and maps to reveal the forgotten contribution of flak in World War II, from doctrine and tactics to combat stories on the ground and in the air about what it was like to fly into the teeth of antiaircraft fire.