Answer: Sky trenches.

Basically you create a giant floating defensive network above a city, that has weapons designed to fire upwards towards the sky. These would be on weapons platforms that perpetually hover above a city or other points of interest in order to protect it from descending attack aircraft. I imagine these platforms would be absolutely massive, like a floating fortress. These would probably look something like this (but with a ton of guns not air-strips);

Those floating fortresses would be able to move and move anywhere they are ordered to, in order to protect said area. Whenever an enemy force descended from the sky a sky trench (or multiple sky trenches) could be floating there waiting to engage them.

Obviously elements of the city owner's interceptors and ground army would be engaged, but the floating fortresses would provide the majority of air defense.

How would this hold up? Why or why not? What would you do differently?

3837575 And when said platform, presumably nuclear-powered goes down it takes out half the city with it. Congrats.

3837594
Nuclear reactors can't reach critical mass, never have reached critical mass, and never will reach critical mass.

3837575
Sky trenches? Those things that the Daleks struggled to breech on Gallifrey? Fuck Yeah!
In all seriousness, this idea would work, but just like real trenches, they would need to be extended so the enemy couldn't simply go around them. On the ground this means going across till you hit impassible terrain, but in the sky there's no such thing, so you'd have to cover the entire sky in these fortresses. Otherwise the enemy can just fly somewhere else, get underneath the trenches and blow them up while the guns on top can do nothing. Or if they have guns on the bottom, they'd risk shelling their own city.

Wouldn't it be much better to simply have large scale weapons mounted on turrets in the city itself backed up by aircraft of some description? The turrets can fire up or horizontally, giving them a better field of fire, while the aircraft can take out targets or force the enemy within range of the guns. Plus as 3837594 says (even if it is unlikely to happen) you then don't have the problem of stuff falling out of the sky and crushing your own city when it was supposed to be protecting you.

3837621

In all seriousness, this idea would work, but just like real trenches, they would need to be extended so the enemy couldn't simply go around them.

Which is why the floating fortresses would be mobile, so they could move as the enemy moves.

Wouldn't it be much better to simply have large scale weapons mounted on turrets in the city itself backed up by aircraft of some description?

"Obviously elements of the city owner's interceptors (aka aircraft of some description) and ground army (aka weapons mounted on turrets on the ground) would be engaged, but the floating fortresses would provide the majority of air defense."

Plus as >> Emperor_Lorenzo says (even if it is unlikely to happen)

If by 'unlikely' you mean scientifically proven to be impossible then yes, you are correct. If a sky fortress is knocked out it will cause damage (even if it doesn't take out an entire city), sure, of course it will. However stuff is always going to fall out of the sky, it's an air battle. With the sky fortresses in place above the city they can prevent that stuff falling out of the sky from being enemy fire.

3837609
The kinetic energy would be enough to take out the city. The radiation wouldn't help, either.
Besides, it's obvious that an inordinate amount of orbital defense weapons would better suffice, anyways. Like, constraining the sum total of a multi-system empire's worth of weapons onto a single planet, type of inordinate.

3837626
Alright fine, dismiss nuclear power for what it's worth, I don't know enough about it to say otherwise (I also apparently can't spell as it took me five attempts to spell otherwise correctly )
First off, mobile platforms. Great, they can move. Now what happens if say the aliens have a large enough force that they can send a third of their force one way, a third the other, and keep the final third heading straight down hmm? To quote Yahtzee, it would be like a double cunted hooker filling in for their triple cunted friend. They'll spread themselves over too many fronts and be picked off piecemeal, and as soon as one group falls, the others will have to content with the enemy fucking shit up from behind their lines.

Next, explosives. Unless we're talking lasers (and even then they can require hazardous chemicals such as in Warhammer 40K) If something goes wrong, the station falls quickly and it crashes in the city with it's ordnance intact, it is not beyond the realms of possibility that said ordnance can be set off somehow, whether by accident, enemy fire or whatever. Then all your shells that were going to protect the city have just exploded and blown it into a crater.

Lastly, these things just won't last if they're protecting the city. Think about it, their job is to stop enemy fire getting through to the city below. Now unless they have shield tech to project a protective bubble over the city, in which case why are the nodes outside the shield, they will be using their own super-structure to absorb incoming enemy fire in a very 'don't worry, I'll stop that bullet with my face' kind of way. That would be horrifically expensive, as these are massive flying fortresses, and unless they are manned entirely by robots (which would open up the way for skilled enemy hackers to takeover your massive defenses) would be up there with one of the worst jobs ever.
'Hey, i want you to help man a giant floating fortress that is going to be a huge target for any enemy and has no way of protecting itself other than really thick armour which will eventually be breeched'.
I don't know about you, but that doesn't make me want to sign up. In the same way the Tiger tank wasn't a practical war machine due to it's size, these would be out-maneuvered by faster aircraft and destroyed from below. They could also be shot to death by spacecraft outside of their range of fire, as the enemy presumably has control of high orbit, and while shots may not be able to go up that high, gravity will ensure that they can sure as hell go down.

In essence, these things would be a great moral boost as they are big things to look at, but in combat they would be slow, becoming bullet magnets, and would be incredibly expensive to produce. Kind of like the Tiger and Tiger 2 were in WW2, while the Panther was the better vehicle, despite being smaller and less heavily armed.

3837575

3837678

Shock troopers (preferably of Canadian origin,

Pfft, what are Canadians gonna do, shoot the aliens with deadly, delicious bullets?

3837691
3837685
Not going to lie, I thought you said of Cadian origin.

In which case, these manly motherfuckers would be much better

3837575 Doctor Who rip-off??

3837641 Hey it's you!
But seriously, I have to concur. Sky Trenches, while a good idea in some aspects, aren't very good in others.
If it's possible to somehow increase it's mobility without sacrificing defence and offense, that would be better. But having a giant floating tank which can only shoot up is dumb, and very impractical. Put some weapons on the sides but underneath is suicide to the place you're defending.

Maybe as an offensive ship this would do well. Instead of stationing them above cities, why not make them apart of an aerial assault squad or something? Just put guns everywhere rather than just on top

3837756
Ah! It's you! Run for your lives!

Why have a floating tank at all? Why not just spend the money on more plains and more ground turrets and forget the whole floating fortress thing? Then the planes can be fast while the ground cannons blast upwards and fill the sky with so much lead that the pencil companies all go out of business.

3837764 Yes that makes more sense.
Ground cannons are the most effective form of aerial defence, along side other forms of airforce. Look at the orbital cannons in Halo! They fuck shit up man. Like they really fuck shit up

3837767
MAC cannons!

3837769
On the ground!
And they're fucking huge!

Like that one on Reach, but bigger!

3837769
Then there's this:
http://halo.wikia.com/wiki/Orbital_Defense_Platform
Wanna defend against aliens? This will do it

3837773
Super MAC cannons then. Even better.
Or any of these:

All of these seem like they'd do the job nicely.

3837781 Nekminit dead
Those things will fuck you up!

That doesn't sound too practical. We should rather get a fleet of these and make sure nothing can even get into Earth's orbit. Or even enter our solar system for that matter...

3837575

That's bullshit.

We need to keep them from even getting into Earth's orbit, or anywhere near it, as some have already said. So, I suggest we build a massive fleet a fleet Romulan Dreadnoughts, with an equallly massive support group of also human-made Klingon battlecriusers, and a slightly smaller squad of Avenger class battleships as a extra firepower. Since all of these ships are compatible with cloaking devices, we could sneak up on them while cloaked so they can't see or detect us, once we're in weapons range, we decloak, and destroy the invading force before they can fight back. Simple.

Dreadnought:

Battlecruiser Group 1:

Battlecruiser Group 2:

Has anyone thought of biological weapons? the whole Versailles treaty is void in space, or humans right only apply to humans?

3837575

>flying carrier

*Screams scientifically*

3838193

>flying carrier

*Screams logistically and tactically*

3838193
3838239

>flying carrier
*screams with geeky glee*

3838456
'Tally ho chaps, follow me'
Captain jumps out of the trench and falls to his death.

Well that idea would suck.

Oh, and WW1 mostly, trenches didn't play much of a part in WW2

Thinking about an alien invasion reminds me why I want our SETI program to be built on spying on aliens instead of communicating with them. I'd rather have aliens not know about this planet than knowing about. So I propose every probe we send should be armed with a nuclear bomb

3837980 Sadly if aliens do come, We don't know what were dealing with.

Why would invaders send attack craft when they can send a rock?

Attack craft are expensive. Rocks are cheap. Attack craft need logistical support and have limited range. Rocks can be thrown from a theoretically infinite distance.

There's also the added bonus that if the defenders do manage to destroy a gigantic asteroid (or a swarm of them) hurtling towards their planet, the invaders can always turn around and go home without having lost anything they actually care about.

So if you are serious about defending your planet, you need anti-rock weaponry.

3837575 would rather have 60 hardened positions around the city instead of all my defences in one place.

3838519
Who said the invaders wan't the complete destruction of Earth? What if they want a resource that can only exist without killing everything?

3838524
Who said they're all in one place? And who said there couldn't be positions on the ground?

3838528 no one

3838528 Then we send our most epic people. Examples include Arnold Schwarzenegger, Chuck Norris, and whoever played Rambo.

3837575

3837980

Has anyone thought of biological weapons? the whole Versailles treaty is void in space, or humans right only apply to humans?

Outer Space Treaty bans weapons of mass destruction. Biological weapons fall under the description of 'weapons of mass destruction.' Get good.