He could replace his losses, which were horrific:The tactics Doolittle chose to employ during the early stages of his 8th Air Force tour bore striking resemblance to those used by Ulysses Grant when he took over the Army of the Potomac in mid 1864: attack, attack, and then, attack again. Grant had the men, the weapons, and the logistical tether to sustain him, while his enemy did not. Doolittle found himself in a similar situation; American logistical support was increasing each month of the war, and he was accumulating a vast armada of aircraft, the likes of which had never been imagined.
The 8th Air Force onslaught began in earnest on “Black Monday,” March 6, 1944, when814bombersand943fighterssortieedforBerlin. KnownasthefirstdaylightraidonBerlin by the Americans, it was technically-speaking, actually the second, as 300-odd bombers had made an attempt to bomb Berlin two days earlier. Up till that time, the March 6th mission constituted the largest combined effort of the war by American forces, and 69 of the 702 bombers that stayed the course that day were shot down, equaling the worst single day losses of the war
But as with Lee after the Wilderness when Grant kept coming after him, it was the beginning of the end for the Luftwaffe:To his airmen’s horror, Doolittle ordered the entire 8th Air Force back to Berlin two days later, on the 8th, then, incredibly, again on the 9th. Yet another mission to Berlin followed on the 22nd. On these second, third and fourth trips to Berlin clouds did not obscure the city, and most of the intended ground targets were at least damaged. During the month of March 1944 the U.S. 8th and 15th Air Forces mounted 18 such combined attacks deep into the German heartland. Although we lost just over 400 bombers and fighters, these losses were replaceable because of the war material and training pipeline coming in from a fully-mobilized United States. American manufacturing capacity was outstripping our adversaries in ever-enlarging numbers.
This is the best explanation of how the Allies came to have complete air superiority by D-Day. There's quite a lot here (including the shocking decline in German aviation fuel), but the idea of Strategic Bombing as effective only when targeting prestige targets (like Berlin) because it forced the defending fighter groups into the air where they were shot down by the escorts. The bomber crews were essentially bait.For the Germans, it was a similar story, but they could not sustain the losses. In March 1944 they lost 357 fighters with another 163 damaged. More importantly, they lost over 300 skilled pilots, all killed in action. These combat-experienced pilots could not be replaced, especially in terms of their valuable experience, which served to erode combat leadership in the air. Between January and June 1944, when the allies landed at Normandy, the German Day Fighter Arm was to lose over 1,000 experienced pilots. The Luftwaffe never recovered from this staggering loss. Unlike our training pipeline, the German training syllabus was hampered by lack of combat-experienced instructors, too little fuel and, therefore, insufficient flight time to train up anything but easy targets for the more well-trained Allied airmen.
It's quite an interesting article, that shows just how ugly war is.