Say an advanced alien civilization has mastered the manufacture and use of super-dense neutronium. They utilize it as the “armored shell”, for lack of a better word, of a military armored vehicle, and have a (magical?) engine that can propel the vehicle at combat speeds.

I read, years ago, Greg Bear’s THE FORGE OF GOD, where aliens dropped neutronium and anti-neutronium onto the earth and the two masses tunneled into earth and eventually met at the core where they went boom. I’m writing a story and came up with this brainstorm—the aliens cut the power to this neutronium car, and it sinks into the ground to a certain depth that they require and they feather up the power to maneuver as they wish. Like a submarine, except through rock, soil, etc. Voila! A different kind of stealthy vehicle! Plus, above gound (AIU)I, any bad guys who even touched the car would rue the day. Come to think of it, it would only have to touch or ram any other vehicle, eh? Or any barrier for that matter. Useful, no?

As I have little military experience, do you think, used in this stealthy, underground manner, that this would be tactically useful? Forex, cruising a couple hundred meters underground, able to pop up at any time or location? Especially against foes of inferior tech, like our present day?

My question is not how such a vehicle would be made. The question is: the tactic of sub surface assets that can maneuver underground as well as our submarines do in the ocean.

Or fogetaboutit. Try something else. :)

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    $\begingroup$ "any bad guys who even touched the car would rue the day" So... how do you build them? $\endgroup$
    – user
    Dec 3, 2016 at 16:58
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    $\begingroup$ No need for antineutronium, outside a neutron star neutronium is radioactive, half life 10 minutes. Any piece of neutronium will blast out energy like a nuke but slower. $\endgroup$ Dec 3, 2016 at 17:14
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    $\begingroup$ Civilization advanced enough to make cars out of neutronium most likely has better ways to deal with enemy infantry - assuming they want to deal with infantry in the first place, because since we are talking about forces capable of destroying planets - yes, that kind of pressure is needed to create neutronium - they most certainly don't need to. $\endgroup$
    – Borsunho
    Dec 3, 2016 at 20:39
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    $\begingroup$ If a mine corridor, in cross section area similar to tank, collapse, buildings above it gets damaged. 100m seems exactly how deep mine shafts are. So... Yes. Probably it would. $\endgroup$
    – Mołot
    Dec 3, 2016 at 20:49
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    $\begingroup$ As for what happens, here's a real-world example: the moving of the whole town of Kiruna in northern Sweden, because of the mining going on there. And that mining is almost certainly being done a whole lot more slowly than meaningful "combat speeds". // cc @Mołot $\endgroup$
    – user
    Dec 4, 2016 at 7:03

2 Answers 2


This is like saying "if you have the full US military at your disposal, will it help you eradicate this group of natives with sticks and stones." Of course it will. Or perhaps "If you were Hulk Hogan, would a leg drop be useful for subduing a half-paralized polio victim who was drunk?" Of course it'd work. Once you are so far above a society that what you do is literally seen as magic, you've kinda already won. With engines like that, you could do almost anything (potentially even do nothing) and win.

That being said, I'd point out that this is anything but stealthy. Presuming you, yourself, are not made of neutronium, this vehicle would have to literally dig a hole for you to pass through as it goes under the surface in "stealth" mode. Shoving rocks out of the way like this is not a quiet operation. Geologists have a term for this sort of movement: earthquakes. Pinpointing your location would not be difficult. In fact, I'd guess it would not be hard to tell if you were present, even without all that fancy sensing equipment they use to determine the yield of a North Korean nuclear test from hundreds of miles away. You'd probably be able to feel it with your feet at a pretty good distance.

  • $\begingroup$ An tank-sized object smashing its way through the earth is equivalent to a continental plate shifting position/colliding head-on with other plates/forming entire mountain ranges and ocean trenches... $\endgroup$ Dec 3, 2016 at 23:38
  • $\begingroup$ I wonder if those geologists could detect, with their instruments, the borer for the Chunnel, or would it be lost in background noise? $\endgroup$ Dec 3, 2016 at 23:48
  • $\begingroup$ @catsteevens We can detect tunnel boring machines 3km away from the dig site. Worth noting is that we tend to sense seismic activity on a logarithmic scale, so its reasonable to detect smaller things on the same scale as giant movements. $\endgroup$
    – Cort Ammon
    Dec 4, 2016 at 1:28
  • $\begingroup$ -Wow, good work on the link. So, they pre-arranged 14 stations to record activity--knew what the borer was, where it was, at a depth of 125 m. How would this work from a depth of 1 kilometer in the fog of war? $\endgroup$ Dec 4, 2016 at 2:10
  • $\begingroup$ @catsteevens To really answer that, we would need a lot more information about the aliens. A tunnel boring machine traveling 10m a day is going to have a very different seismic spectra than a tank carving its way through rock at a thousand times that speed. We'd need to better understand how the aliens are using the tank (after all, they've already got the war won, they don't need to go through rock with that sort of tech) $\endgroup$
    – Cort Ammon
    Dec 4, 2016 at 5:23

If you have the ability to stabilize neutronium, why would you need to make a battle vehicle out of it?

First off, why are you fighting on the surface of a planet? If you have the ability to simply create neutronium objects (1 cubic meter weighs $4\times10^{17}$ kg, or about the mass of a ~40 km wide asteroid, why not just throw it at the planet and scour it of life?

If you want to conquer the planet instead of destroying it, why would you not just threaten the inhabitants with death from above unless they do what you want?

The limitation of a battle vehicle is that it can be only in one place at one time. If you send your battle tank to destroy the American Army, then it takes forever because the American army is spread all over the world and then you still need to destroy the Chinese, Russian, British, etc armies. Surely there is a more creative solution for all that energy and technology than one vehicle.

I do not think such a vehicle is either strategically or tatically viable. If you have such great technology, surely there is a better way to fight a war than making uber-tanks.

  • $\begingroup$ Hmm... an armor plate one molecule wide of neutronium could possibly suffice? $\endgroup$ Dec 3, 2016 at 19:30
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    $\begingroup$ @catsteevens Still, the point is, a civilization that can make neturonium can surely think of some better ways to fight a war than running tanks around. Engineering viruses to kill their enemies? EMPing the planets electronics back to the middle ages? Using super-science to mind control everyone? $\endgroup$
    – kingledion
    Dec 3, 2016 at 19:34
  • $\begingroup$ And what if they could build thousands? I mentioned a small Infantry Fighting Vehicle, tasked with hauling foot soldiers around, not laying waste to continents. Your IFV has steel armor proof against small arms fire, theirs has an impenetrable barrier against anything you could throw at them, plus can attack from below. :) $\endgroup$ Dec 3, 2016 at 19:40
  • $\begingroup$ @catsteevens No, you did not mention an "Infantry Fighting Vehicle". You mentioned an "IFV". Please don't assume that everyone is familiar with uncommon abbreviations. $\endgroup$
    – user
    Dec 4, 2016 at 7:05

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