Lets discuss!
And just to be clear, this means what you consider the most impressive from the pilot's view. Meaning it is more impressive if the pilot has to dodge lots of obstacles, fight high command, ect ect... to land a bomb that did nothing for the war in reality. Important bombings might be included, but the fact that they were important is not considered a positive characteristic in itself (then it would be 'Most Important').
So my vote is the bombing of the Shell-house in Copenhagen in WWII.
The Shell-house is smackdown in the middle of central Copenhagen, and it was the central HQ of the Gestapo, containing many resistance prisoners (many slated for execution). Of course it was a nice target, but the Germans didn't expect it to be in trouble, as any bombers would be spotted long before they were in range (and intercepted by any fighters), and it was in the middle of a densely populated area of occupied people. Further it was protected by civilian buildings all round more or less.
So mass bombing was out of the question to just hit this target. And a few bombers were easy to pick off with the local fighters. The Germans were right to feel secure.
A flight of Mosquitos were selected for the bombing. They had to avoid land all the way to Copenhagen (a major detour around the north), and do this at sea level (something that woul come back to haunt them).
Anyway they did manage to sneak in under the radar and entered the city at such a low level that some of them knocked over chimneys, and people claimed that they flew below the rooftops (in the streets).
So the approach to the target was bad enough, but at the target they were not allowed to just bomb the building as the prisoners were not to be killed. They had in fact been placed in the upper storeys as a failsafe for bombing.
So the planes had to bomb the lower levels of the building.
Eventually they did line up when disaster struck.
The leading plane got shot down (or struck a structure on the way I don't know) and the next plane in line had his windshield so plastered with salt from the sea that he had a hard time making out the target, so he just targeted the the explosion of the leading plane's bombs. Sadly, it had crashed into the French School, so the following plane bombed the school killing about 40 children and teachers. But the next planes managed to line up correctly and left their bombs at the door, leading to a most unpleasant day for the doorkeep.
The result was an astounding success since most of the captives not only survived but managed to escape in the confusion.
Pretty impressive in my mind.
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