I will go first, a stealth tank

Its only stealthy at night (they just painted it black)

They forgot to take the LED lights off.
- It's to be stealthy during day

A rifle scope that can see through walls.

It does this by 'inverting' what can be seen through.
It can't see through air.
- You win
It has a negative magnification: it's a fisheye lens.
- My personal winner
- Fisheye lens is fractional magnification, negative magnification is mirror
You can see through more than walls, you can see through everything! ...so all you can see is the empty void
It only works if it's pointed toward Chernobyl
Granted. The scope can see though a wall after you penetrate it with bullets (the wall, not the scope).
Rifle can't shoot through walls.

A weapon system that spreads peace, love, and freedom indiscriminately.

Indiscriminately across all of space and time... which is mostly empty.
- So when it averages out, it's actually less effective than cat videos.
- Something something Romans and fields
Reavers.
- No power in the verse can stop me

An army of hive-mind cats.

The plan works perfectly. You are not in charge of the hive mind.
Tear gas has been converted to cat nip gas.
They're all still behave like a normal cat.
I just want to express my desire for an army of attack cats trained to shred anything painted by a laser, designator, pointer or otherwise
- Be the change you wish to see in the world
- Good news, I have a prototype.
It's nap time... it's always nap time.
Is it somehow different from regualr cats?

An APC that only needs the power of the sun to run; no fuels.

It needs the power of the whole Sun
The battery for the solar panels is so big, there's only space for a driver and one passenger
- Armored Person Carrier
It can only move 1 inch per hour.
It needs an actual sun inside.
Granted. It's a wagon train.
Solar panels are not armored.

It’s a plug in hybrid and silent like a Prius under 5mph.

It uses a standard US household wall plug (hard wired to the vehicle), and is extremely loud above 5mph.
- US household wall plug
  Now this is evil
- It takes 23hrs to get 1hr drive time
Max reverse speed is also capped at 5mph.
- Max rollback before automatic brake application of 5mm

A sword that appears in your hand whenever you need it, and then disappears again when you don't.

In appears IN your hand, ripping your muscles and tearing your skin
Your hand ends up looking like you played with super glue and fireworks
Also, you can only summon it twice before you run out of hands
- Heh, also you don't "summon" it... it appears whenever you need it.
It appears while being held by the blade.
- Weren't origianl knight longswords held by blade?
  wiki longsword
  If it's not factual blame Bones heard it from them.

A gauntlet that lets you control metal like magneto.

You can't uncontrol it
- Haha holy shit I love this one so much
- Anti-ejecto seato cuz, ride or die!
The gauntlet is also metal, and gets attracted to your hand squeezing it until it breaks your bones every time you use it.

it's AI controlled

That's a downside - imagine an AI that can't draw trying to differenciate between a friend of foe. it just shoots everyone and their cat
Tay is back, bitches, and she has a a heavy autoloading cannon
The AI watched The Iron Giant and loved it.

A button that makes the backdoor in enemy C&C softwere.

The backdoor gives you access to the enemy's copy of C&C: Red Alert.
....turns out the latest upgrade to your c and c software was stolen from the enemy by cyber squad, and most of your assets on the southern front are now controlled by five primary school cs:go players in Fulham.
It's spotted within 5 minutes by some nerd who noticed that the program took an extra ten seconds to load and immediately wanted to know why.
- It was chinese backdoor. Russian backdoor will make it load in 10 seconds less.
- 10s? Pfft, amateur; the xz backdoor caused a ~500ms delay in SSH logins and somebody went "hmm that's weird"
The backdoor is locked

Dima, Ivan, I need weapon from you that only hurts bad guys!

The device fails because moral relativism (as discussed by philosophers like Gilbert Harman) and the complexity of ethical theories (such as utilitarianism by John Stuart Mill and deontology by Immanuel Kant) make it impossible for a machine to accurately judge "bad" actions or intentions, given the deep subjectivity and cultural variance in ethics.
it only hurts them, cannot actually incapacitate or kill them. you have a torture device. task failed successfully?
Weapon guidance system never miss comrade. System trained with Ivan 100,000 times.
The weapon only kills Russians

A gun that switched everyone's gender but not their sex.

It always fires twice in rapid succession
...it also affected the Fatherland.
Somehow, it works the opposite way changing sex but not gender identity

Too stealthy. Crews can't find it.

Its sitting in the exact same spot as the Doomturtle, theyll find it eventually.

It can pierce through any armor.

But only if no one is wearing it.
But only the armor. Bullet passes through helmet, stops when it hits skull.
The ejection of the carriage kills the gunner, every reload.
Use machinegun to cut holes in tanks and throw grenades in them

Robotic Christopher Walken.

Can't walk
- Christopher Rollin.
He just wants to be... ...human
... oh, did you want him gigantic, or armored, or something?

a hydrogen powered artillery cannon with 2 kamikazi drones equipped

The hydrogen can only be inserted in solid form by hand
- i thought someone wad going to do something with the drones
fuel tank cracks when the gun fires

Stealth tank skin requires full stripping and recoating after anything hits it to remain stealthy.

Repairs take too long because even in a busted state it's still very hard to spot.

Quantum Tunneling Neutron Cluster Railgun capable of assassinating a target from the opposite side of the earth at slightly less than the speed of light.

Main problem is nobody made optics that can see to the opposite side of the planet. Personally, I think we should just take the direct route and fire it through the planet but the egghead sciency types keep complaining about "destabilizing the earths crust". Whatever that means.
- That's actually not a bad downside, it still pierces literally any armor if you can guess the distance and point it at the target by sight. I'll take 5,000 for $6.4 Million each, send the invoice to Congress.
  Imagine taking shots in the dark at the Kremlin and exploding random furniture and windows. Putin: "That's the third time this week, we have to move offices around again."
Has the power requirement of the sun though.
- In the palm of my hand?
Good luck aiming.
Aliens already have that technology, and they're determined to prevent any other species from developing it. They zap your prototype and research facility from orbit.

An anti radiation missile that targets passive systems

it uses nuclear power for fuel and keeps shooting itself

My dick, but it's armored.

Pee hole is vented backwards
You feel absolutely nothing.
- You thought after he armored up his dick he'd still use it to fuck?
- I imagine anyone that wants an armored dick can't feel anything all ready.
The armor is retained by a 20cm long tube inserted in urethra

They make: open wagons, flat wagons, tank cars and tanks.

A Knife which looks like a Gun but is also A Gun which looks like a Knife.