59

Assuming that the object is to protect earth, and not just hide away when the aliens come... Join the Department of Extraterrestrial Defense The Department was founded in the sixties, at the same time as the project to create a psychic supersoldier using LSD. Currently it consists of one insane bearded guy, in the 22nd basement level of the Pentagon. ...


54

Impractical At the height of their trajectory the soldiers have no vertical movement so if this coincided with the top of the battlements they would land like a feather. True, their vertical movement would be zero, but what about their horizontal movement? There are three types of arcs (roughly) if you want to talk ballistic weapons. You have a mortar-type ...


52

Aliens are few and far between, drones do the work and are trivially replaceable. The aliens are using drones for the day-to-day movement of force on the planet. There are only a few alien beings, and they're safe in their spaceship on the edge of the solar system out of nuke range. The drones can be destroyed en mass by organised military but are trivially ...


48

The virus is a strategic mistake The virus was released into the atmosphere, so unevenly and dependent on winds, the carnage will spread, quickly, but some survivalists, politicians, military, etc with bunkers with air filtration will get into their bunkers and wait it out. Not many, but there will be a few uninfected ready to come out 2 weeks later at full ...


45

why invade at all? Most structures of a civilisation are probably going to be on a surface. It is, after all, more difficult to build underground than on a surface. That means that most items of value can be simply blasted from above. But you might not want to blast them from orbit because these items might also be of value to you. You might want to avoid ...


45

They can't At least not from Mars itself A radio signal will take between 5 to 20 minutes to go directly from Earth to Mars and back. That makes for a round trip time of between 10 to 40 minutes. So even supposing that: Your martian hackers have gone through the DNS part (i.e.: the venusians provided them the IP 172.217.13.206, which is one of the valid ...


44

There are a couple good answers already about how Paul can help the world prepare by sharing knowledge, or advancing technology. But if he is really prepared to consider any option, to take any action, there are at least a couple more options he should consider, whether or not he actually decides on using them. Take up Super-villainy Honestly, there is ...


43

Annexation can be defensive in nature. Alien race A may know of an impending invasion from alien race B, and are attempting to annex Earth to protect it. Alien race B is out to conquer new worlds but knows that if it attacks part of alien race A's empire, a large-scale war would break out and race B would suffer greatly. Annexation by race A would serve ...


30

Yes A nuclear sub can spend six months underwater and have 135 crew. There is about 150 around the world. You then have the virologists and other scientists working sterile labs would work out what the issue was really fast and protect themselves You have the military personnel working in bunkers with filtration designed to resist biological attacks. You ...


30

How feasible is it with medieval machinery? Very feasible. Trebuchets were a thing in Europe around the 6th century AD and are very calibrable (yes, this is a word). What, if anything, is wrong with this idea? Murphy's Law, and not just how you imagined it when you read it. Edward A. Murphy Jr. was working on project MX981 (a spiritual predecessor to ...


29

Keep in mind that an alien civilization might have a concept of ethics and morals which is completely different from ours and completely incomprehensible from our perspective. They might have evolved into a centralized, non-violent hierarchy millennia before they even developed technology. A decentralized system with independent countries and organization ...


29

From Mars: One 4K Netflix Movie per Unconditional Surrender The real answer is provided in the next section, with the use of probes, but here is the physical reason why it is impossible to access the internet directly from Mars: signal strength loss. Regardless of how the Aliens receive weak signals from Earth, the Aliens will still need to send signals to ...


29

The aliens don't care much about interaction with the general populace, and don't have supply chains Guerilla warfare works because people can melt back into native populations and because logistics are tricky. You can ambush small groups as they move across unfamiliar territory, attack weaker supply lines, use civilians as a cover for assault. So, the easy ...


28

One Ship (and not even a very big one) If they have the tech to travel the stars, they have the tech for biological weapons. If they can make and use biological weapons, they can spray it into the atmosphere and wait to clean up the stragglers. We wouldn't even have to know they were here. Do it right and make some ethnic specific targeting viruses the ...


27

This has been done many times. The European colonisation efforts in India, Africa and Polynesia amongst others are very well documented, but many outfits did the same. Basically you provide weapons and perhaps training and expertise to one side to defeat the other in their own interests. Then pick a reason to wipe out the first. Or just arm the remnants of ...


24

They need to get local. Current (actively used) internet protocols are simply incapable of dealing with the light-lag delay between Earth and Mars. Even if they could somehow build a powerful enough wireless transceiver to connect to WiFi or other internet-carrying signals, ping times of >40 minutes simply wouldn't work. If the aliens want to interact ...


23

Sir, here is your Prime Commander with an extensive report on our position. We are not reciving support The empire has, once again, refused to send more soldier to help us, saying that for those puny humans our flotilla should be more than enough and, as commander @Zhehao pointed out, FTL is too expensive anyway. We are on our own. High power weaponry I'm ...


23

Don’t drop one asteroid. Drop thousands The mathematics of impacts is fairly well understood (though it is a little fuzzy at high speeds). For any given weight and shape of ‘asteroid’ (really an aerodynamically shaped, ceramic coated lump of rock with some engines attached) hitting the ground at any given speed: You can quite accurately predict the blast ...


20

Invent it. Big changes have taken place in the US, I gather. If there are thousands of superintelligent AIs milling about to be conscripted, over previous years there were probably other issues involving AIs and semisentitent automatons. You can invent your government agency to deal with these. Heck, The Department of Motherland Security was only ...


19

Stealing a little from @DJClayworth's answer, this answer is probably too self-insert-fan-fiction-y to make a good story, but it is exactly what I would do: Tell Carl Sagan On September 28, 1980, PBS aired the first episode of Carl Sagan's Cosmos. It quickly became the most-watched American television program of all time for a decade until it was ...


18

Please note that this answer was submitted before the question was edited to include the new 'Accepted Answer' conditions. The aliens are a parasitic race The aliens land in cities all over the world and demand that everyone submit to one specific test - an anal probe. When asked why, all they will answer is - "It is necessary for the survival of ...


17

The Fleet They Have Is Good Enough To Conquer Earth, At Least For Some Definitions of Conquer In chess, there are two kinds of attacks. There is an actual attack, i.e. rook takes bishop, and then there are the threat of an attack - moving a rook so it threatens a bishop. If you ask an amateur player which of the two is better, they'll likely say the first, ...


16

Can't beat em? Join em! Your refugees contact a selected Earth government. They ask for help. They say that they are fleeing their dead world and need a place to live. They have advanced tech they are willing to share. Plus they are xenocurious humanoid hotties who only wear skin tight silver lamé space jump suits. There is no government on Earth that ...


16

Engineer a virus specifically targeted to kill humans which is very contagious and has a long gestation time, say 6 months. Introduce it into various cities around the world and let it spread invisibly. Wait 6 months and watch the majority of the human world population vanish. Sprinkle it on the remaining patches of human settlement to finish the job.


14

Just one ship: Land on the far side of the moon and start mining thousands of rocks. This means setting up the launching infrastructure. So...a base. Launch a couple thousand rocks, timed for simultaneous impact. Includes destroying all retaliatory capabilty (ICBMs, launch sites, etc) The bigger the first strike, the better. Consider spending years ...


14

It is usually determined by (1) numbers, (2) unequal levels of civilization and (3) particular situations in each case. If the conquerors are much fewer than the conquered, or if the conquerors are barbarians and the conquered are much more advanced in civilization and technology, or if the conquerors didn't bring women with them, then it almost certain ...


14

You already did it: Guerilla bands are but one form of asymmetric warfare. It occurs when there is a large gap in the capabilies of the two sides. Guerilla warfare is, at the core, a desperation measure by one side to avoid complete collapse, to demonstrate their continued relevance to the population in otherwise-enemy-dominated territory, to preserve ...


13

Swarm and flock members follow very simple rules that let them maneuver in concert with the others. They use the perceived rate of change in speed and orientation of their most immediate neighbors. http://www.red3d.com/cwr/boids/ If the aliens adopt such a pattern of flight, it's a strong indication that they follow similar rules, with comparable inputs. ...


12

Before the Cold War began, aliens attempted their first invasion. This would have been around the end of WWII, over Germany. The aliens actually struck Berlin and shredded most of the Nazi party. The Battle of Berlin was actually the first battle against the aliens. Hitler's body was never found because the allies didn't kill him - he had already been taken ...


12

28 Days Later: This virus has a distinctly familiar sound to it. Like that virus, there are several exceptions that need to be looked at. First, your virus is extremely lethal. That means it will have a hard time spreading. A sick person on a plane will start attacking people immediately, and the plane would be quarantined (if it even made it to the airport)....


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