There's a lot of short stories and sci-fi movies depicting stealth alien invasion, typically on American country village or even a big city. We're not talking war with advanced sci-fi tehcnology - we're talking about hostile alien species, typically more deadly and vile than any predatory species on Earth. And of course they are inexplicably interested in killing or eating humans specifically. Best example is the Alien from the alien franchise, but there are hundreds of variations on this kind. Unlike alien invasions, they come in small numbers initially, but multiply drastically, presumably in abandoned underground structures.

Let's narrow the circumstances now. We have several unsettling deaths and disappearances in a big city. Finally, one happens in front of police street camera (no witnesses that time or ever before, the public is simply not aware of this), clearly displaying that innocent pedestrian was attacked by something quite obviously alien. Or at least, the alien assumption has the benefit of the doubt.

Typically, upon discovery of alien threat, fictional stories focus on the protagonists and make the army appear lame, unprepared or absent completely. This does initially work since the media consumer focuses on the story as well, but later comes as not so thought through.

My question here (emphasised since people seem to disregard this paragraph) is how would realistic, real-life police react to this evidence, as an organisation. What procedures should be followed? What would be done to verify the threat? If verified beyond doubt (eg. alien nest is found), what would be the next steps from the government's army? Are there any international protocols that would take place as well? How is the public treated, and how fast?

I'm not looking for ideas how would theoretically some government react. I am looking for information as factual as possible on the measures intended to deal with unknown lethal alien threat - all that is there to know and is not military secret. US military allegedly has protocols for dealing with zombie apocalypse, so I assume they are prepared for everything. Note also that, especially for benefit of other visitors, answers definitely do not need to focus on US in any way.

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    $\begingroup$ Try a freedom of information request. Bristol City Council responded to one about the zombie apocalypse so you never know. (Yes, it's real) $\endgroup$
    – Separatrix
    Jul 13, 2016 at 9:01
  • $\begingroup$ Is the information made public? $\endgroup$ Jul 13, 2016 at 9:53
  • $\begingroup$ @AmiralPatate I don't know, that's why I ask. $\endgroup$ Jul 13, 2016 at 10:33
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    $\begingroup$ The response largely does depend on the country, and even the location within said country. For example, European cities are much more tightly packed together, the population is not nearly as well armed, and their military forces are not nearly as combat-ready. In the US the response is guaranteed to involve a heavy military reaction, whereas in some European countries (which I will rephrain from naming) I could easily see the debate devolving into an animal rights issue while thousands die. $\endgroup$
    – AndreiROM
    Jul 13, 2016 at 17:30
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    $\begingroup$ Are your aliens intelligent or just animals? Is their Earthy equivalent a cannibalistic serial killer or a man-eating lion? I'm asking because movie monsters always behave like smart-as-humans serial killers, even when they are meant to be dumb-as-rocks lions. For instance, movie monsters kill and kill and kill, but never stop to eat! They don't eat at the kill site, nor do they feed on Monday, then return on Tuesday to eat some more. They never attack where there's CCTV. They don't lie around basking in the sun, like lions or crocs. How your alien behaves will dictate how the cops/army cope. $\endgroup$
    – DrBob
    Jul 14, 2016 at 12:32

6 Answers 6


Overwhelming response.

Just look at how police respond to known dangerous threats like a guy driving around shooting cops (Dorner, for example) or an active shooter. They mobilize EVERYONE, kick down doors, and shoot anything that even remotely looks hostile. This response, be it against a human, animal, or "WTF?" would fundamentally be the same. Basically throw bodies at the problem until it is resolved.

  1. Block entry/egress.
  2. Quarantine folks inside the perimeter until they can be documented, searched, and cleared. They may be held in temporary holding areas to get them clear of the threat.
  3. Probe the area with scout teams, drones, dogs. Go door to door, clearing buildings one by one with teams on overwatch.
  4. If/when a hostile presence is found/suspected, gather as many folks as possible and force entry (unless they know it can talk back). Shoot until the threat is non-threatening.
  5. Keep searching until all areas are clear.
  6. Clean up.

Obviously the team required will depend on the time available and the search area. A single building with an active threat? The cops on duty right now. A city block and the threat is unknown? A majority of the force. Several days and a threat the cops encountered and couldn't deal with? Call the Feds and the Governor may active the National Guard to bring in big guns. This will take several days though. Using an active duty military unit on US soil is tricky, so you can't just dial up the 101st and have Blackhawks flying in an hour. Obviously given the evidence (big slimy tentacled horror on the street or whatever) a form of Martial Law/suspension of Posse Comitatus by Presidental Order would bring in military units pretty damn quick.

There are no "contingency plans" to whip out for every little situation like this. There doesn't need to be, as the same plan will work for alien infestation as for a terrorist cell, wacko cult, zombie outbreak, demons from hell, or whatever. The tools are largely the same and the people available to execute the plan are the same.

Surround the threat and shoot it into compliance :)

An alien event would probably be treated most like a chemical/radiological attack; with the use of protective clothing, decontamination of anyone in the area, collection of samples for testing, etc. We do have stockpiles of stuff for this in FEMA stores and military bases, most larger police departments probably have some in a dusty closet somewhere. Look up "CBRNE response" (Chemical Biological Radiological Nuclear Explosive) to get an idea of what it may look like.

Now you can debate whether or not there are DETECTION teams scattered around, like NEST teams monitoring for radioactive materials or biological detectors. Is there a government "alien hunter" unit that investigates strange occurrences? Possibly, but there definitely isn't some elite unit that trains for these things (that have never actually happened) because those guys can be used in actual events like hostage situations and terrorist attacks.

  • $\begingroup$ I think this is a somewhat optimistic scenario. $\endgroup$
    – AndreiROM
    Jul 13, 2016 at 17:25
  • $\begingroup$ Realistically you're going to get a lot of disbelief, fear, uncertainty, unprepared individuals in leadership positions not sure how to react, etc. Will this footage leak to the media and cause widespread panic? Will it remain in government hands, and trigger a very silent hunt for those predators while more people die? Will some extremists (think PETA) get involved and try to "save" these creatures (maybe by pulling favor in government)? How will all these factors come together to affect the outcome? Difficult to say, but such an effective and organized response is highly unlikely. $\endgroup$
    – AndreiROM
    Jul 13, 2016 at 17:35
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    $\begingroup$ I don't think so, not for a few organisms running around in a city. Now if a giant landing craft, complete with air cover and war machines, beached down in some city park, perhaps everyone will flee. But otherwise I think cops (and soldiers if available) will cowboy up. Not really a lot of superstition these days and most folks have a pretty strong belief (extremely well founded as it turns out) that enough bullets will put down anything. Modern urban warfare tactics are designed to minimize personal risk and force almost reflexive behavior which will help suppress fear of an unknown target. $\endgroup$
    – Jason K
    Jul 13, 2016 at 17:50
  • $\begingroup$ "most folks have a pretty strong belief (extremely well founded as it turns out) that enough bullets will put down anything" <- that made me lol. I largely agree, although I'd like to know what inspired the "extremely well founded as it turns out" bit. I guess my issue with your vision is how casually you envision police forces stepping up to deal with this issue. $\endgroup$
    – AndreiROM
    Jul 13, 2016 at 17:57
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    $\begingroup$ Hard to say, really. Is a tentacled monstrosity any more terrifying than a grizzly bear, big croc, masked gunman, or burning skyscraper? I think folks can severely disconnect their fear when they are about to go to war. Getting all armored up can do that as well, it has a buffering effect. Then you add in a stack of guys, lots of lights, commo in your ear, etc and it is easy to disassociate yourself from what you are doing. Fundamentally the alien response isn't any different than responding to a terrestrial threat. At least on paper.... $\endgroup$
    – Jason K
    Jul 13, 2016 at 18:28

This depends heavily on many factors, especially the alien's biology. While many of the other (optimistic) answers would hold true for roughly human-sized, squishy aliens, you have to remember that even on Earth, not all species behave like that. They could be large or small, thick or thin. Most likely, the military response for any such threat would involve a rapid evacuation. Aggressive military response would have to wait until people could start innovating new defenses for an unknown threat. Virtually all able countries would lend a hand quite quickly. Except Australia.

Massive individual creatures

Let's say large enough that the young are on the order of magnitude in size as a modern elephant. These creatures would certainly cause some tremendous panic, but the bigger they are, the harder they fall. Unless they have some special defense mechanism like releasing thousands of tones of toxic gas, they could be taken down pretty quickly by a few fighter jets.

Human-sized, squishy creatures

Anything around the size of a human with squishy flesh would be the most stereotypical alien. They would effectively be nothing more than really foreign predators. An individual could easily be taken down by brute force alone. A small mob of guys with knives and hammers, half a dozen guys with handguns, or a couple of trained police officers could take one down easily. These creatures would be no problem for the military.

Even so, like other squishy threats, no matter how much effort is taken in defeating them, all that could be done is control them to an acceptable level. An individual alien or group of aliens like this could be taken out easily by police, trivially by the military, but finding them all would be an issue.

The military is pretty adept at killing squishy, human-sized creatures. Gee, I wonder why?

Human-sized, shelled creatures

This is where it starts to get interesting. A creature around our size but with a thick exoskeleton or shell would be able to resist virtually all projectiles. If it's strong enough, they could potentially resist fairly powerful explosives, too. A creature with armor composing 70% of its dry mass would not be particularly easy to kill with guns.

Small, numerous creatures

Sure, shooting something tends to incapacitate it, but have you ever tried firing into a swarm of locusts? What about locusts that are highly intelligent and can spit boiling acid? The military response may involve incendiary weapons, which may or may not have any effect. Before any of that happens though, there would be an incredible mass panic that hampers evacuation. A large city could experience significant losses before the situation could be put under control, even with the knowledge of the creature's weaknesses. This situation could very well cause incredible damage to all of humanity, depending on the level of dedication of these creatures (whether they really, really want to hunt humans down, or whether they just opportunistically feed on humans where they find them).

school of fish

Aren't you glad these little guys don't bite, and confine themselves to the ocean?

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    $\begingroup$ Do you have any examples of actual protocols that explain what a government would do in real life, as opposed to how easy it would be for them to deal with the threat? $\endgroup$ Dec 11, 2017 at 9:48

I'm ignoring the Brookings Report entirely, as it only raises questions. But aside from that there is the SETI Post-Detection subcommittee:

A Post-Detection Subcommittee has been established, to replace the Post-Detection Science and Technology Subcommittee which existed under the former IAA SETI Committee.

Chair: Paul Davies, USA
Deputy Chair: Carol Oliver, Australia


And the UN initiative:

The United Nations is about to appoint a little-known Malaysian astrophysicist to head its Office for Outer Space Affairs, which could soon be designated with the task of communicating with extraterrestrials. Mazlan Othman will tell delegates to a scientific conference next week at a country house outside London that she will head the UN office and be in charge of talking to any aliens who either arrive here from another world or, more likely, communicate with us.


The United Nations Office of Outer Space Affairs (UNOOSA) has announced that it will consider drafting protocols for what to do when we finally make contact with extra-terrestrial civilizations in space.


Sad to have to debunk the zombie plan:

The zombie plan, otherwise known as CONPLAN 8888-11 or “Counter-Zombie Dominance,” is actually just an in-house training tool to help teach students how to understand “basic concepts of military plans, and order development,” a Navy spokeswoman told Foreign Policy.


  • $\begingroup$ Not sure how this answers the question. Sure, there's a bunch of commissions and councils are out there (which mostly came into being due to an abundance of caution), but realistically I don't think any of them are prepared - or have the mandate - to take command of the armed forces of any given country and impose certain strategies such as martial law, nuking a potential infestation site, etc. $\endgroup$
    – AndreiROM
    Jul 13, 2016 at 17:31
  • $\begingroup$ @AndreiROM It's actually useful to at least know which other parties may be involved, especially in the aftermath. $\endgroup$ Jul 14, 2016 at 7:58
  • $\begingroup$ @TomášZato - ok, i see your point. $\endgroup$
    – AndreiROM
    Jul 14, 2016 at 13:28

You ask that we provide a general answer as to how the world would react to such creatures, but it would largely depend on the country this is taking place in, and even the city.

For example, the US is a very militarized country, and each state governor has the ability to declare martial law and call in the National Guard. That's a pretty big advantage over most European countries where the military is not quite as prepared to answer internally (IMO).

Other major variables are whether this footage leaks online, or whether it remains within government hands, and is made secret.

So, having warned you that there's a lot of room for interpretation, I will give you my opinion on what the sequence of events in such a situation would be:

The Setup

Following the first few deaths specialists in wildlife attacks would have been called in to asses the remains and try to identify the species responsible. I am going to assume that these experts will have immediately realized that something is wrong.

Maybe an autopsy will even reveal strange liquids, bits of skin, or fragments of teeth, etc. left on the body.

Aware that something is very suspicious the authorities would next get access to the video.

The Video

Now there's an indication that the attackers are never before encountered creatures. There may exist some question as to whether the video is a hoax, but I'm sure such suspicions would be discarded soon enough.

At this point you can bet that high profile politicians (the mayor, state governor/equivalent, maybe the president/premier) are also involved. As soon as this outbreak is confirmed (drones finding such a creature, their nest, or some other proof) their first thoughts are going to be:

  • Do these things carry any infections or diseases we need to be aware of?
  • How do they breed?
  • How do we contain them?


At this point the military will 100% be involved, whether under some pretext, or through an honest aknowledgement of the issue at hand. Martial law is basically a guarantee, and some evacuations are also probable.

They will be investigating the possibility of containment, as well as the nature of the creatures, although armed response is also possible based on how steady the number of murders is holding.

Depending on the nature of the creatures (how quickly they breed, how widespread they are, how intelligent, and able to oppose human forces) containment may well be very difficult.

For example, the Xenomorphs are highly intelligent, incredibly powerful, and - through various tactics - have wiped out armed human soldiers with ease before. They would not win out against all of humanity, but they may well deceive, evade, and eventually inflict major casualties on our military forces. A dumber, more feral foe may not pose as great a threat in the long run.

If these things to prove as aggressive and dangerous as you say then a decision to wipe them out is going to be implemented sooner rather than later. Think teams of soldiers equipped with flame throwers, etc. A nuclear option is also likely to be held in reserve.


Realistically, humanity will win out against such creatures. There's too many of us, and we are way too gifted at killing things. Even if we are caught unprepared, we will eventually develop highly specialized equipment to deal with the threat.

The only major variable is how many would die before we got organized, and whether it would come down to using large scale bombardments, chemical weapons, or even nukes to stem the initial outbreak.


Legally, the only protection an alien would have would be whatever the animal cruelty laws provide but since this would be a first contact event, the authorities will have to assume that it's intelligent and would probably invoke whatever first contact protocols they have. I'm not aware of official US policy in that regard, the closest thing we have is the NASA commissioned Brookings Report which has a section on first contact scenarios. I read somewhere that the UN is thinking about drafting such a document but I don't know if that ever happened.

In terms of public safety, they'll probably evacuate the civilian population and quarantine the area then try to communicate with the alien.

The details will vary from country to country but in most places the executive branch (President/PM/Highest military commanders) will take the lead. Marshal law for the affected areas is likely.


Probably the same as major terrorist attacks, military attacks or large-scale wild animal threats. Alien incursions would combine all three.

SWAT teams and ambulances will be the first responders. Eventually the different levels of the military will join in.

The USA has a National Counterterrorism Strategy, the FBI and the CDC, especially to counteract chemical and biological attacks, does too. The main problem may be coordinating all the relevant agencies that will rush into the fray when an alien incursion happens.

It might be more profitable to choose a location, say, Painesville, Ohio, and drop your alien incursion into there and then look at what law enforcement services, military forces are available in that area and its surroundings. Trace what communications are available for sending out the message to the wider world that aliens are here now. That is unless puts a giant force-field dome over Painesville, Ohio, and keeps everybody trapped inside.

  • $\begingroup$ No force shield. The way how is this transmitted to outer world is also part of the question (but not how the world reacts). I was expecting more specific answer honestly. $\endgroup$ Jul 14, 2016 at 13:54
  • $\begingroup$ Sorry. The force-field dome was only a bad joke. Frankly for more specific answers I suggest talking to people who deal with these situations. The closest equivalent to an alien incursion is mass violence or a disaster or a terrorist attack like the lone wolf shooters. Otherwise we're all second guessing what the professionals would do. That's why i suggested choose an actual place for the incursion and ask the relevant authorities. Usually they're cool even with way-out requests like this. $\endgroup$
    – a4android
    Jul 15, 2016 at 7:03
  • $\begingroup$ I'm sure some police officers, soldiers or other goverment officials too use stack exchange. I never implied everyone must be competent to fully answer this question. I'll try to reach out to someone in person, but it's - you know - much faster and easier to ask a SO question first. $\endgroup$ Jul 15, 2016 at 9:04

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