On October 14, 1943, almost 300 B-17s made a second attempt to destroy the ball-bearing factories in Schweinfurt, Germany after a disasterous first attack on August 17. The B-17s were escorted by P-47 Thunderbolts up until the Thunderbolts reached the limit of their range and had to return home, leaving the fleet to continue unprotected for three hours until reaching their target. only 229 reached Schweinfurt, and on the return, the German fighters had landed, refueled and rearmed and attacked the retreating fleet again. The battle demonstrated to the allies the importance of fighter escorts with sufficient range and the vulnerability of heavy bombers against interceptors.