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Comment by msdz | Hacker News Reader

> 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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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...

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.

You're looking for Young's penetration equations, developed at Sandia National Lab in the 90s. Your favorite LLM can walk through the math step by step if you're interested, but a US WW2 era AN-M64 500 lb bomb gives results of 15-20 ft penetration in average soil. Reality might be a little less because free-falling bombs have forward velocity from the aircraft that dropped them, so they hit at angle instead of penetrating straight down.

And Berlin is not known for hard soils.

The scarier one for me is this happened with a nuclear warhead in I think Carolina, it was buried in impact without going off, and they never found the core

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