As a German living in Berlin it's still pretty normal that once in a while WW2 bombs are found during construction. Heavy bombs that didn't explode probably penetrated the ground quite a bit so when rebuilding it was probably just easier to just leave them there. That's just a guess.

There are also still bombs and grenades in the rivers. There are some magnet fishing YouTube channels where you can occasionally see them pulling up stuff like that.

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msdz 3 hours ago | parent [-]

> so when rebuilding it was probably just easier to just leave them there. That's just a guess.

My take (equally guessed): Among the literal rubble spread all over the cities, people constructing everything back up with whatever means possible couldn’t even recognize a mostly buried object as a bomb (instead of just more scrap from a collapsed building).

So less of an active decision to not deal with it, rather one out of necessity and/or not knowing about them, perhaps?

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GolfPopper 2 hours ago | parent [-]

My own guess is that a fair number of them just buried themselves. While I don't have all the relevant facts at hand, per the US Naval Institute, a 550 lb bomb dropped form 20,000 feet would hit the ground at 880 feet per second [1]. If my rusty mind is correct, that would be around 9 megajoules, while feels like it ought to be enough to bury a bomb pretty well in any sort of yielding soil.

1. https://www.usni.org/magazines/proceedings/1941/december/how...

	▲	usrusr an hour ago \| parent [-]
		Have another bomb in the vicinity that did not fail and there will be absolutely no visible indication at all that something penetrated the ground. I might be imagining this but I think that I have seen a report about some systematic effort to trace bomb dropping patterns in aerial images of the aftermath to find gaps in the pattern where something did not go off. But no idea how early or late after the war that happened (if it did happen). And those patterns will only show up for smaller bombs dropped in quantity, not for the big ones.