In Weapons for a civilisation-destroying giant robot I asked about what weapons might be placed on a sixty-billion-ton fusion-powered snakebot 9.27 km long and 1.19 km in diameter, armoured with 224 metres of Boron-Carbide surfaced Tungsten-Depleted Uranium alloy armour.

The snakebot is equipped with a multitude of sensors on its skin, including optical sensors from the far UV to the far IR, electromagnetic sensors, audio sensors (for what it matters given that it would most likely have to stop moving to hear anything) and radiological sensors. It also has broad-band radar and lidar capabilities. While these sensors are surface-mounted, they may be retracted for defensive purposes (and to protect them if the snakebot rolls), and replacements are available further beneath the armour in case of battle damage.

The snakebot is armed with hundreds of "small" railguns dispersed over its outer armour, each firing a steel optically-self-guided flechette about 18mm in diameter and 288mm long at velocities of around 5000 metres per second, at around two rounds per second.

It is also armed with six large railguns in its "mouth", only one of which is available for use at any time, the others being retained deeper beneath the mouth's armour as immediate-use backups, firing 144mm diameter, 2304mm long optically-self-guided munitions at a velocity of around 7000 metres per second, at about 40 rounds per minute. These munitions may be single depleted-uranium long-rod penetrators, or they may be capable of breaking up into hundreds of unguided steel sub munitions at some point prior to impact.

Resupply of these munitions (except for the depleted uranium munitions, which would be used sparingly) would be by the expedient of the snakebot "eating" ferrous human infrastructure and processing it into more ammunition.

The snakebot is supported by a multitude of nanite-controlled birds which act as its spies. The controlled birds act naturally as far as possible, and each bird stays within its species' natural range. They will not attack and neither will they defend themselves from attack beyond those defences typically used by their species.

Prior to commencement of the attack, the snakebot's nanites have also tapped into the public internet, however, they cannot rapidly decrypt secure communications, not being equipped with quantum computers (unlike their military nanite brethren, which were not deployed on this mission).

Using this information, the Snakebot has been tasked to destroy all human infrastructure significantly more advanced than a shack or a tent, and to defend itself against counter-attack. Its target priority is to attack targets in the most militarily-capable areas first.

It is not interested in exterminating humanity. Individual humans are of little interest to it unless they are counter-attacking with any effectiveness, at which point the snakebot will simply eliminate the threat in the most expeditious manner possible given its options. However, neither will it attempt to preserve the life of humans or any other species.

If damaged, the snakebot's controlling nanites will use whatever materials available within the machine's structure and in the environment to effect repairs. The snakebot took around ten years to build beneath the Antarctic ice-cap, and the time to repair damage can be expected to be roughly inversely proportional to the amount of damage - the more damage, the more nanites will be required to repair it, and conversely the slower the repairs will be. Relatively minor damage can be expected to take as little as a few hours, and major damage such as the total loss of one reactor can be expected to take many months to a year or more.

When the snakebot has destroyed all modern human infrastructure (i.e. anything more advanced than a shack or a tent), or it is incapacitated to the point where it cannot continue its mission at all without first effecting repairs, the snakebot and all the engineering nanites on earth, including those controlling birds, will self-destruct. Don't worry, the birds won't be significantly harmed by their controlling nanites, either while being controlled or when the nanites controlling them self-destruct.

Any nanites captured by humans will self-destruct, of course.

The question:

Given the entire military and civilian resources of the modern world (like we wouldn't unite to get rid of this thing) , how can the Snakebot of Doom be defeated, or are we destined to be reduced to living in crude lean-tos and tents until we can rebuild our civilisation?

  • $\begingroup$ Is the Snakebot shielded against Electromagnetic pulses? How long does humanity have before Snakebot of Doom snakebots us all? $\endgroup$ – vanillagod Mar 2 '16 at 9:23
  • $\begingroup$ i really like the way that this incorporates my answer while also improving and expanding on it. nice work! $\endgroup$ – Duncan Urquhart Mar 2 '16 at 12:37
  • $\begingroup$ The small railgun projectiles don't much work. An 18 mm front optical element won't work for long ranges, and at short range self-guiding is both unnecessary and inefficient due to the short flight time. Plus, while scavenging iron from the ruins has its attractions for resupply/replenishment, fabbing the optical seeker/guidance/steering elements is much more difficult. Not to mention the fact that a 1.2 km diameter construct will be very inefficient at harvesting surface materials - frontal area vs ground collection area ratio is too high. $\endgroup$ – WhatRoughBeast Mar 2 '16 at 14:50
  • $\begingroup$ Somebody already had that idea, and made an app: colossatron.com $\endgroup$ – Mindwin Mar 2 '16 at 20:35
  • $\begingroup$ Also, you should [reality-check] your snake's size and weight. $\endgroup$ – Mindwin Mar 2 '16 at 20:36

The Snakebot will defeat itself by its excessive density.

The snakebot has a volume of around $10.3 \text{km}^2 = 1.03×10^{10} \text{m}^2$. Given its mass of $6×10^{13}\text{kg}$, this means a solid cylinder with a density of $\text{5.8 tons/m}^3$. This is denser than titanium at $\text{4.5 tons/m}^3$, but less dense than iron at $\text{7.8 tons/m}^3$

However, this will mean that the snakebot will be unable to move on almost all types of terrain. Given that the snakebot has a maximum ground area of $11\text{km}^2$ (length x width), its minimum ground pressure assuming all of its available surface area is contacting the ground would be an immense $6×10^{13}/1.1×10^7 = 5.5×10^{6}\text{kg/m}^2 = 55\text{MPa}$. This is greater than the pressure exerted by bullets on their target, and the pressure that bombs exert on buildings.

For comparison, the German WWII Maus tank had a ground pressure of merely 0.14MPa, and it quickly sank into the ground during its field trials.

These calculations are assuming perfect conditions, with the snakebot at rest and not exerting additional pressure on the ground. It will sink even in those perfect conditions, and therefore it is unlikely to be an effective tool due to its inability to move effectively.

  • $\begingroup$ Not just on land. Since water is only about 1 ton/m^3 even underwater it would sink and once on the ocean bottom it would act very much similar minus 1 tons/m^3 $\endgroup$ – Murphy Mar 2 '16 at 12:58
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    $\begingroup$ It's actually worse. You missed the kg-f to Newton conversion. 1 kg in a 1 g field produces a force of 9.8 Newtons. So the best-case pressure is 550 MPa. Since the compression strength of granite is about 130 MPa, the Snakebot will sink inexorably from sight. Also, the linked question establishes that the Snakebot will move by eating its tail, forming a torus and rolling. Maximum footprint in that configuration is about 1/3 your assumption, so the ground pressure goes to the vicinity of 1500 MPa. $\endgroup$ – WhatRoughBeast Mar 2 '16 at 19:53
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    $\begingroup$ @MontyWild - Square-cube. It's the law. $\endgroup$ – WhatRoughBeast Mar 2 '16 at 21:29
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    $\begingroup$ @MarchHo - I meant that as the structure size increases its volume and mass increase as the cube of the dimensions, but the support area only increases as the square. So at some point, the material under the structure fails and cannot support it. However, as long as the density of the object remains less than the surrounding material it will float. So the square-cube law provides for the sinking of an object as long as it is above a certain size. $\endgroup$ – WhatRoughBeast Mar 3 '16 at 0:00
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    $\begingroup$ I kind of hate to say this, but I think your physics is wrong or more like incomplete. The worm will sink until it reaches hydrostatic equilibrium, that is the pressure it applies to rock under it (55MPa?) equals the ambient pressure at that depth. I think this is around 2km? So if immobile the worm would eventually create a lake few hundred meters deep for it to hide and wait. Since the rock would resist the deformation this would take a long time and the depth the worm sinks to would depend on its speed. So faster it moves, the less it has time to sink and the faster it can move, LOL. $\endgroup$ – Ville Niemi Mar 3 '16 at 1:18


Is the snake from space? because given these numbers it contains more weight of material than all the worlds recoverable iron reserves, all the worlds known uranium reserves and all the worlds known tungsten reserves.


"armoured with 224 metres of Boron-Carbide surfaced Tungsten-Depleted Uranium alloy armour"

The armor would be a problem, even for a nuclear weapon.

Lets compare to the tsar bomba, the largest nuclear weapon ever detonated. The explosion left a crater 6,500 feet (2,000 m) in diameter and 250 feet (76 m) in depth. Notice that 76 meter depth in only normal stone/earth. Even if the tsar bomba was physically sitting on top of the thing... it would hurt it but probably wouldn't get through the armor.

That being said, repeatedly detonating large nuclear weapons as close to it as possible would burn away surface weapons and reduce it's ability to fight.

Feed it the Tsar Bomba

Of course detonating against the armor is a little like setting off a firework on your open palm. What you want is to get the thing to wrap itself around the weapon.

It's already eating everything it can find, get a big, disguised nuclear weapon into it's mouth and under the armor then set it off.

Boring answer, stand well back and leave it to rust, declare any area in range of it's weapons an exclusion zone, it can barely move

When an object undergoes a proportional increase in size, its new volume is proportional to the cube of the multiplier and its new surface area is proportional to the square of the multiplier.

For example, if you double the size (measured by edge length) of a cube, its surface area is quadrupled, and its volume is increased to eight times its original volume.

The point of this law is that with living beings, strength is (more or less) a function of area (the strength of a muscle or bone is proportional to the area of its cross-section, not to its total volume), but weight is a function of volume. And Newton's famous Second Law (the "force = mass × acceleration" one) means that if you double a critter's height while keeping it the same shape, you end up with four times the muscle power moving eight times the mass, so instead of having the same relative agility as the original, the double-sized creature actually has only half. The same goes for most machinery.

AKA, it's pretty much impossible to move a metal structure over a kilometer high weighing 60 billion tons with pretty much anything.

Any motor would burn out, any internal cables would snap. if this thing moves at all it will be like a glacier giving the world lots of time to prepare shaped nuclear charges, Rods From God etc.

It won't be able to lift it's own weight with any motors or mechanisms made out of normal physical matter.

  • $\begingroup$ It's only 1.12k high, not 2km. Diameter, not radius. $\endgroup$ – Separatrix Mar 2 '16 at 12:38
  • $\begingroup$ You're right, corrected. $\endgroup$ – Murphy Mar 2 '16 at 12:46
  • $\begingroup$ Also, you might consider the EMP effects. $\endgroup$ – WhatRoughBeast Mar 2 '16 at 20:01
  • $\begingroup$ I think EMP gets overstated in fiction. Most of the thing is inside a grounded metal shell and totally immune to any EMP. $\endgroup$ – Murphy Mar 2 '16 at 20:14
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    $\begingroup$ +1 Rods from the Gods. That's one of my all time favorite ways to wreak havoc from orbit. $\endgroup$ – Green Mar 2 '16 at 21:22


Since it is tasked with destroying all human structures, such structures essentially act as bait to attract it to the area. It shouldn't be that difficult to cover a suitable area with dense enough mine field to guarantee a hit. After all the snake is fairly wide. Likewise since the size and armor require the mine to be very powerful it can be placed deep enough to make detection by the snake unlikely. After all the ground will be covered in debris and fractures caused by the snake and its destruction. Likewise a target this heavy will be easily detectable from significant depth simply by its ground pressure.

Given that there would be some pressure to deal with the snake fast, I'd assume the mine would actually be a large number of nuclear warheads dumped together in deep hole that is then filled with reinforced concrete. It wouldn't be as good as really building a very large warhead, but if any one of the warheads goes off being contained underground should cause all the warheads to go off with acceptable efficiency.

Naturally an explosion powerful enough to destroy the snake (or damage it enough to make it vulnerable to "clean up") would cause lots of collateral damage, I'd imagine a super volcano would be a good comparison. So people would probably need lots of time to accept it is necessary. So if the snake prioritized destroying the nuclear arsenals, it might be able to prevent this approach.

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    $\begingroup$ A nuke detonating will destroy another nuclear warhead, not detonate it. A nuclear detonation relies upon a symmetric conventional explosion of almost ridiculous precision, and to subject a warhead to an asymmetric blast would simply smash it, not detonate it. The warheads would have to be synchronised to a similar precision, though if you can do that for one nuke, you can certainly use the same technique to synchronise multiple nukes. The set-up time would simply be longer than you might have anticipated. $\endgroup$ – Monty Wild Mar 2 '16 at 22:30
  • $\begingroup$ @MontyWild That is not strictly true. Yes, above ground and uncontained EM radiation will impact the other bombs first and make a sympathetic detonation nearly impossible. But deep underground in a closely contained space neither the energy nor the material can escape fast enough, so the fusion reaction should be triggered. Which in turn should release enough neutrons to trigger fission. And yes, there is lots of speculation in that. Not sure if anyone has even actually researched it beyond making sure it can't happen in facilities used to store the warheads. $\endgroup$ – Ville Niemi Mar 2 '16 at 23:59
  • $\begingroup$ That would be too speculative in the face of such a large threat. Better to spend the extra hours synchronising detonation and know that all the nukes will contribute fully to the blast than to dump, run and pray. $\endgroup$ – Monty Wild Mar 3 '16 at 0:28
  • $\begingroup$ @MontyWild True enough, there is no reason not to synchronize them. I actually remember thinking about explicitly writing that you should have multiple triggers each triggering multiple warheads for redundancy, but in the end skipped doing so as being too much detail. $\endgroup$ – Ville Niemi Mar 3 '16 at 1:23

the first thing i thought of after answering the other question was that it would still be vulnerable to a few things. like Niemi said, using mines or other concealed weapons would possibly work, but you could say the sensors like the robot detect and disarm/avoid them in advance. another solution that would actually end up being easier than trying to nuke it directly would be to use the EMP burst from a nuclear weapon detonated in the atmosphere above it to take out its systems. however, hardening the doombots systems would be trivial for such a powerful species, so that option is probably out. honestly, the only thing that might work is using something that it cant dodge or shoot down, like lasers or kinetic orbital bombardment. neither of these exist in any useful or usable capacity at the moment.

side note: i really like the feeling that the possessed birds add on to the "mythology" of the snake. it really makes it feel less like a evil robot and more like some vengeful and unknowable god that has awakened from its frozen slumber.


The best way to defeat a snake is from the air. Even with railgun weaponry etc, we are talking about a mass of hundreds of thousands of tons just for the head, which is a lot of inertia. The snake cannot move rapidly enough to get away from air launched munitions.

As mentioned in the earlier question, modern munitions have ranges of over 100km from the launching aircraft, so the Defenders of Earth (have that as the Squadron name: pilots will be fighting each other in bars to join!) can start harassing the beast from a great distance. A wide variety of ordinance can be used, from rockets and guided missiles to armour piercing glide bombs. The use of a wide range of ordinance will overwhelm the capabilities of the defence, both in trying to spoof various guidance mechanisms (although how hard is it to miss a target 9 km long?) and being able to engage literally hundreds of weapons in the air coming at a full 360 degrees of coverage. The various munitions will be arriving with all manner of speeds and altitudes as well, from Mach 5 "Sunburn" anti ship missiles to leisurely Small Diameter Bomb glide bomb attacks.

Now this assumes the various governments of Earth are either not willing to release nuclear weapons or don't trust the Defenders of Earth squadron, so the most powerful weapons that the snake could face are massive "bunker busters" designed to penetrate solid rock, reinforced concrete and alternating layers of protection to destroy deeply buried command posts and facilities, and thermobaric weapons, which deliver heat and shockwaves that can also crush heavily defended structures. This in addition to the more conventional flocks of high explosive weapons raining down on the target.

If the incoming weapons are not enough to immobilize and disable the snake, then any strategically sized nuclear weapon will be employed.


For some reason I watch this snake bot quest line with interest... and finally I thing I found its lethal weakness: heat.

Airborne Laser

Or frome space... anyway, while a short shot will do nothing, you could melt away any form of armor with ease if you manage to heat it up. Even better - microwave it. No need for any optical energy loss, just keep Terawatts of microwaves firing upon it. After you didn't mention a Faraday's cage, this will roast any electronics inside... buuuut at least tungsten and uranium are metals, so it will shield the interns. And they are fine heat conductors and heat capacitors, if I recall right.

Your outer hull does have a melting point of about 3000 Kelvin, that next layer might come around 3500 Kelvin... that are peanuts for a laser.

To be honest, you would need to do this for a long time, and the "eat a tsar" from Murphy is probably the faster solution, but it would be a pain in the ass getting that bomb inside it. Even more - it does not need to eat anything, just keep on moving to destroy something.

So I recommend a combined action: insert a fusion power plant inside a 747, and let it aim for the railguns, wait for snakes maintenance stop, keep on heating it up until something starts glowing red, than drop that cute nuke at this location. Hole in the wall. Now you can melt anything inside.

That does sound easy in theory... most difficult part would be creating a laser / maser that is powerful enough.


So while I'm unsure what a dozend meter of superheavy metals can do against an emp, it something you could try at least and look whats happening. At least the railguns will provide a point of attack for any form of em shock therapy...

EDIT: Ou, someone did mention the emp-idea while I was typing already. credits for him if this is the solution.

  • $\begingroup$ Where does the fusion plant come from? We don't have them yet, and the one we're trying to build certainly won't fit on a 747. $\endgroup$ – Monty Wild Mar 2 '16 at 22:32

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