The generals in charge only changed their minds when the US 8th Airforce was almost completely destroyed in a brief series of fierce air battles over Germany.
On 17 August 1943, in what is known as the Schweinfurt–Regensburg raid, 60 US bombers were shot down, 20% of the attacking force. Another 100 bombers were so badly damaged they had to be scrapped.
The Americans had received such a bloody nose that the 8th did not fly a deep penetration mission again for three weeks.
On 6 September 1943, during a raid on Stuttgart, 45 US bombers went down in flames - 17% of the attacking force.
On 8 September 1943, thirty bombers went down in a raid on Bremen - a loss of 8% of the attacking force.
On 9 September 1943, in a raid on Anklam-Marienburg, 28 US bombers were shot down - a loss of 8% of the attacking force.
On 10 September 1943, 30 bombers went down in flames during a raid on Munster. That was 13% of the attacking force.
On 14 October, the US 8th Air Force flew a mission known as the Second Raid on Schweinfurt, the location of Germany's main ball bearing manufacturing plants. 60 US bombers were shot from the sky - 26% of the attacking force.
Over a two month period, 148 four engine US bombers had been shot down, almost 40% of the US bombers in England. More than that number had been so badly shot up they had to be scrapped. There wasn't much left to the 8th Air Force. Nor was there much left of the theory that bombers could execute missions over enemy territory without long range fighter escort.
Hap Arnold, commander of the USAAF, ordered that a long range fighter be produced and operational within six months.
It is worth noting that in US infantry units in World War Two, three men were wounded for every man who was killed. In the US Army Air Force, three men were killed for every man who was wounded.
Sources: To Command the Sky: the Battle for Air Superiority Over Germany, 1942-1944 by Stephen L McFarland and Wesley Phillips Newton (3 stars) and Masters of the Air: America's Bomber Boys Who Fought the Air War Against Nazi Germany by Donald L. Miller.
[Images courtesy of the National Museum of the US Air Force.]