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My aunt lives in Hamm, Germany. It used to be a massive rail road hub and allies bombed the f* out it. The old church sitting middle of the town still carries the scars of bombing. Few years ago, during the renovation of the shopping mall, construction crew found unexploded American 500 lbs bomb in the ground. City had to evacuate a lot of people. Throughout years, there were multiple other incidents with UXO in Hamm, that I can recall. I still wonder how the 500 pound bomb been sitting in the ground so many years, right in the center of the town, right by the shopping mall and no one noticed.

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About 10 years ago somebody found an unexploded shell/cannon ball from the war of 1812 in Boston Harbor while poking around during an astronomically low tide. The bomb squad detonated it on the beach in my neighborhood (most likely a training exercise hard to know how dangerous it was). Still upset I missed it. At the time I lived in an apartment where I could see the detonation site.

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.

> 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?

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.

Yeah, bombs are found regularly. A special case was about 15 years ago when there was a bomb in Munich they couldn't diffuse and which in consequence has been exploded purposly right in the city: https://m.youtube.com/watch?v=dJwE2wLJKKc

That was a quite impressive experience. Windows in the surrounding area broke and straw, which they used to damlen the shockwave, caught fire and was thrown around.

10 - 20 % never exploded, and those exploding buried the unexploded ordnance. https://www.alamy.com/stock-photo-bomb-craters-after-allied-...

Those areas where moon craters at the end of the war. But by then logistics where decentralized, all those last days last ditch products, where made in underground facilities or small village smith factories. Effectively they bombed a bomb disposal pit..

True further east, here in former Germany, now Poland. Especially throughout the construction and investment boom that's been happening since 00's. Just last year my neighborhood was evacuated.

Unexploded Soviet ordnance - insane how much of it was dropped and buried in the rubble to this day. You're right though - weird to think that nobody would notice, but so much Europe was turned to rubble at that time. These things got turned to unrecognizable rusty mush after a few decades.

Pretty sure it's also an excuse to keep the bomb squad and evacuation procedures in practice. These things are pretty routine, there is no fear or panic. IThey just diffuse and take the thing away to some military range to dispose of it.

Defuse. Diffuse has a different meaning.

"Pretty sure it's also an excuse to keep the bomb squad and evacuation procedures in practice."

Definitely not in this eastern part of germany where I live. Every major construction needs to check for bombs, but it also happens randomly that a excavator finds a bomb.

There were just a looot of bombs dropped. (And they don't always move it, often it is too rusty also to defuse and then controlled explosion if the surroundings allow it (they use lots of water bags on top, witnessed it once))

>Definitely not in this eastern part of Germany where I live.

A farmer or construction worker (or at least one outside of Germany or any other culture famed for incessant rule following) only needs to watch the bomb squad guy rip a shell out of the ground with a shovel and no specific care given once before they realize it's best if they just do that damn job themselves and avoid the hassle.

Hm, but they maybe know when it is safe to do so, because they immediately recognize the device and know there is no mechanical fuze that can go off by handling it rough.

Because that can happen. And if they know, it still can go wrong.

From TFA:

"In June 2010, three bomb-disposal experts in Göttingen, Germany, were killed by a 500kg American bomb found beneath the site of a new sports arena. "

https://www.theguardian.com/world/2010/jun/02/germany-bomb-w...

> only needs to watch the bomb squad guy rip a shell out of the ground with a shovel and no specific care given once before they realize it's best if they just do that damn job themselves

Do you apply this logic to surgery, engineering, etc.?

"The expert makes it look easy, therefore it must be easy."

I know it's really easy to make this out to be big and scary and complex from your ivory tower but the person doing this has already seated a tractor tire with starting fluid, used a forklift as a work platform, welded up the leak on the air compressor and half a dozen other things that you said would kill them that day and it's not even noon. Using the leaf blower and a broom to dig an artillery shell that didn't go off 5min ago when you hit it with a piece of machinery isn't that much of a stretch. These people live in a different (better) world than you.

Please make sure they put your HN username in the obit so I can read it from the “don’t touch the unstable WWII bomb without knowing how to manage it” ivory tower.

It really is very common here in Germany to get an alarm that a WW2 bomb was found somewhere near you, telling people close by to evacuate. Like every couple of months. It doesn’t even register with people, I don’t know if the news even report it.

Germany deals with multiple thousands of WW2 bombs each year to this day.

For Berlin you can really imagine how much bombs were dropped if you look at the aerial images from the 50s. You can find them on their Geoportal. if you click on the dots there is a link to see the oblique aerial image to get even a better feeling.

Link Aerial image: https://gdi.berlin.de/viewer/main/?MAPS={"center":[390416.44...

Link example oblique aerial image: https://gdi.berlin.de/data/luftbild_1954_sl/pictures/1954_sl...

9 years ago in Thessaloniki Greece, another 500 pound bomb was found 70000 people were evacuated, the disarming took 30 minutes reportedly. Last week they found 1000 pieces of various unexploded ordnance in the city's harbor, leading theory is they were dumbed during the German withdrawal in the second world war.

> I still wonder how...

A 500 lbs bomb falling from altitude can bury itself a fair ways in soil. Most of its fellow bombs will have good fuses - and with the mess they make, it would take some careful excavation in just the right spot to find the dud bomb. (Or, maybe it fell in a patch of overgrown brush in a park, or in a river, or a farmer's pond, or ...)

And with the scale at which Germany was bombed in WWII, there was nothing remotely resembling the resources to carefully excavate all the myriad square miles where dud bombs might have fallen. Either during the war, or after.

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