A very unhappy "what didn't" was that an effective long range escort was not developed sooner. And what is most tragic is that that escort WAS IN ENGLAND in the summer of 1942. That was the P38.
There was a P38 group sent to England; shortly it was detailed to North Africa.
The P-38 would and could have been MUCH more effective as an escort than it was, and earlier than it was.
As many may not know, the P-38 was plagued by mechanical problems that limited its effectiveness. I don't recall the exact problems, but they caused the lead to separate out of the gasoline, causing detonation, and engine failure. A re-designed carburator --later-- fixed the problem. As it was, even a few dozen P-38's made a big difference in breaking up the German fighter attacks on the bomber boxes. But the technical problems were not given top priority, and no large P-38 force was built up in '42-'43. Some DID go to Guadalcanal. Great thinking.
The big wigs in England just kept bulling ahead, thinking they were killing the German day fighter force, when that just wasn't happening. They seemed to think the bomber boxes were these flying buzz saws that would wreck the German fighter force. Black Thursday was the final wake up call. The 8th had lost 45 Forts on a raid to Munster the week previous to 14 October, '43.
It was finally an assistant secretary of War that came out to England in the Summer of '43 that got the ball rolling faster on the redesigned Mustang.
But the Germans had defeated the day bomber as of 10/14/43.
Walt