On 17 Aug 1943, the 8th AF sent a maximum effort mission to demolish the Schweinfurt (ball-bearings) and Regensburg (Bf 109 assembly) factories. This was the deepest penetration yet of the heavy bombers inside Germany…and one that after the Belgium-Netherlands border would lack fighter escort.

376 B-17 took off from England, 361 were effective sorties (15 returned early -4%-) bombing both targets. The massive Regensburg factory was hard hit (but it was far from destroyed). 5,000 workers were working the shift when the bombs started falling and 402 people died -8%-). Messerschmitt started to disperse its factory immediately to the Obertraubling airfield which eventually had 11500 workers. The Schweinfurt bombing was more disappointing. 80 bombs landed on the premises out of 954 aimed (8%) and only one department in one out of 3 factories bombed received major damage. Production of ball bearings in September exceeded those of August. Dispersal efforts were minimal.

301 B-17 returned to friendly bases (but 11 of those were written off). 60 Bombers were shot down by the German defenses (83% by fighters), so overall 71 B-17 were destroyed or damaged beyond repair (almost 19% loss) and 162 returned with repairable damage (43%).

Sometimes this raid is pictured as if the German fighters and Allied fighters did not engage because the Luftwaffe waited to attack the bombers after the escorts left. In reality, the Germans started their attack soon after the Dutch coast was crossed when the bombers still had their P-47 escort and ended it when the B-17 were leaving it protected by the P-47s. The Luftwaffe lost 47 fighters (20 Bf109, 18 Fw 190, and 9 Bf 110) shot down or damaged beyond repair, of which 5 of which were lost in accidents, out of 540 sorties flown (8.8%). 21 were lost to B-17 gunners and 21 to allied fighters (13 shot down by P-47s -11 by 56FG, see picture-, and 8 by Spitfires). The Germans lost 16 KIA and 9 WIA among the aircrews.

Seven Allied fighters were lost (3 P-47s and 2 Spitfires from the escort, and 1 Typhoon and 1 Spitfire from diversionary raids).
The Allies thus lost 78 a/c that day (out of 376 bombing sorties, 456 escort sorties, and 469 diversionary sorties -1301 total or 6%-) losing 114 KIA, 393 POW, and 39 evaders (546 MIA). Another 19 were WIA (apparently).
The USAAF claimed 307 German fighters destroyed (288 by bombers, 20 by P-47. Overclaim ratio of 14:1 and 1.5:1 respectively).

Even though the Germans reduced fighter pilot training in Oct 1942, the bulk of the pilots had been trained with the previous syllabus and were as good as their allied counterparts. It would be until Oct 1943 when some fighter wings would start to notice the lower quality of the new pilots (it took about a year to train pilots).

This raid resulted in the first major tactical defeat of the 8th AF.