On 14 October 1943—forever after known as "Black Thursday"—the Eighth Air Force dispatched 291 B-17 Flying Fortresses to smash the ball-bearing factories at Schweinfurt, the industrial heart of Germany’s war machine. After P-47 escorts turned back at the German border, the bomber formations fought a running battle alone against a Luftwaffe wielding rockets and cannon. Sixty bombers were shot down over enemy territory; another seventeen crashed or were scrapped on return, and 121 more limped back riddled with holes. Nearly 600 Airmen were lost. The shock of the losses forced USAAF leaders to suspend deep penetrations beyond fighter escort until the P-51 Mustang arrived in force. It was the crucible that proved unescorted daylight bombing could not survive over the Reich.