
Hunting submarines with magnets - miraj
http://www.economist.com/news/science-and-technology/21709948-new-way-detect-even-quietest-boats-hunting-submarines-magnets
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willvarfar
Ah, I thought it might be an article about the magnets that the Canadians
literally dropped on submarines! [https://warisboring.com/nato-bombed-soviet-
submarines-with-t...](https://warisboring.com/nato-bombed-soviet-submarines-
with-tiny-annoying-magnets-ba11cfb5578d)

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cowardlydragon
Oh, they gave them up because they were too effective on subs in training?

This is a ludicrous article. NATO must have these ready and waiting.

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philip1209
If this works, that would be cool. However, these defense contractors are
incentivized to make it seem like something is working so that they beat other
contractors to follow-on funding. That doesn't necessarily mean that they are
close to making it production-ready for a Navy boat.

SQUID is tough technology. It takes liquid nitrogen or liquid helium to get
them cold enough to superconduct. A tank of liquid nitrogen is easy enough to
take on a boat, though.

The devices are so sensitive that you can rotate a cheap one 90 degrees and
easily measure the earth's magnetic field. Advanced ones are used to measure
brain wave activity. My concern is that SQUID devices are so sensitive that
they cannot be stabilized enough on a boat in the ocean to prevent noise (from
Earth, boats, gyroscopes, liquid nitrogen pumps, etc) that would make it able
to consistently detect the Debye effect.

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deutronium
This may be an incredibly stupid question, but I know they used gravimeters to
map the ocean floor on subs.

And I recall an anecdote of snow fall on a roof effecting their results in a
lab, could you possibly use them to detect other subs.

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brandmeyer
If it is based solely on mass, then I don't think so. A submerged submarine is
almost neutrally buoyant[0]. It has the same average density as the water
around it. Therefore, the mass of the ship is the same as the mass of the
water it displaces, and a gravimeter wouldn't observe anything different.

[0] Err, almost. There is no such thing as perfectly neutral buoyancy. In
practice, they are very slightly heavy and fly though the water as a lifting
body.

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deutronium
Cheers! That's a very good point.

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djyaz1200
From space...
[https://en.wikipedia.org/wiki/Swarm_(spacecraft)](https://en.wikipedia.org/wiki/Swarm_\(spacecraft\))

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rdtsc
My computer science teacher in high school was a sailor in the Soviet Navy. He
alluded to something like this being used. That would have been in the min 90s
or so. At that point we weren't part of the empire so he probably didn't care
about keeping the secrets about it.

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dfc
The article mentions an article from 1990 in the Soviet military magazine
"Naval Collection."

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rdtsc
Yap, saw it. The way he talked about it sounded more like a "it already works
in practice this way" vs "it could work in theory". But I maybe
misremembering, it was a long time ago.

