If Russia isn't planning to invade, their efforts have backfired spectacularly.
Ukraine has been begging the US and UK for the latest gen anti tank missiles, the famous Javelin and less famous, but equally devastating NLAW missile systems for years now. These are infantry weapons that can reliably defeat any tank Russia has. Ukraine has been facing off against Russian tanks in the Donbas conflict and suffering terribly, and these weapons would go a long way toward evening the odds there.
The US and UK have until now largely refused to sell Ukraine these weapons (and Ukraine has offered to pay way over the market price), out of fear it will escalate the Donbas conflict. Ukraine says it needs these weapons to defend itself if Russia tries to invade Ukraine proper, but the US/UK have taken the view that if Russia ever did that, it will take Russia months to move so much troops and equipment and will be caught by spy satellites, leaving plenty of time to rush those Javelins/NLAWs to Ukraine.
I cannot overstate how badly Ukraine wants these weapons. They begged and begged president Trump for Javelins, the entire debacle over the infamous Trump "Ukraine call"/"quid pro quo" thing, and indeed the allegations around Clinton/Biden interfering in Ukraine (I don't really want to get into either of those debates right now though please) were all about those missiles and what Ukraine would be prepared to do to receive them. Getting those missiles is Ukraine's number one foreign policy goal.
Until now, they have only received (I believe) 30 launchers and 180 Javelin missiles from the US, and nothing from the UK, with strict terms on when and where those Javelins can be used. Basically enough to tell Ukraine to fuck off and stop asking us for them all the time.
Well now Russia has spent the last few months doing exactly what the US/UK said would be make or break time for sending missiles to Ukraine. And the UK (and I suspect the US with greater secrecy) have indeed followed through on their tacit promise to get Ukraine those missiles if that situation were ever to arise.
If Russia weren't planning to actually invade, this could be the biggest fuckup by Russia since... idk... Operation Barbarossa? (Edit: since this post blew up overnight and some people mentioned it, the fuck up was the Soviets being so unprepared for Barbarossa. I'm well aware it was a German operation) The UK in the last few days has transported 1,500+ NLAWs and counting to Ukraine. Between bouts of intense sweating and nausea at the prospect of all out war with Russia, Ukrainian leaders must at least be able to enjoy the occasional wry smile at that.
Any Russian invasion will now take devastating casualties to their vehicles, as a lone Ukrainian infantryman crawling through a bombed out building, thicket of trees, ditch, etc only has to get within 600m of a Russian tank to blow it to smithereens. Worse still, even if Russia backs down and doesn't invade, expect Ukraine to use NLAWs in Donbas from now on. And while many have pointed out that these missiles won't help Ukraine against Russian air supremacy much, they're missing the point: air power is mostly useful against large targets, not widely dispersed soldiers armed with missile launchers.
That's why these missiles are so important. Ukraine has plenty of tanks. Ukraine has plenty of artillery pieces. Expect them to be destroyed by Russian aircraft in the opening hours of the invasion. But there are 200,000 Ukrainian infantry (plus a million or so reservists) who until recently couldn't really do much but run away against tanks so weren't really a problem for Russia. Now they can. Russia would still win an invasion, but is likely to lose 100s of tanks, and leave many infantry units without effective tank support, enabling Ukrainian infantry to stand their ground better, driving up the human and equipment cost to Russia of such an invasion dramatically.
I'm convinced Russia didn't actually expect the UK/US to make good with the missiles to Ukraine. Russia probably expected indecision, political fluff, and fear of provoking Russia to paralyse them into inaction. If so, they badly miscalculated.
But it's difficult to see what Russia expected to achieve if it had no intention of invading. The economic cost of relocating ~150,000 soldiers, along with massive numbers of tanks, aircraft etc from all across Russia (Russia has pulled units from all over Russia to spread the shortfall in other regions equally), building field hospitals, supply dumps, staging grounds, etc is enormous. The Russian stock market has also taken a big hit. It's a huge cost to pay for a joke/empty threat, even without it handing Ukraine a tremendous victory without a shot being fired.
This is why I think this is likely going to be a real invasion. Or at least, it was before the UK floored everyone with their response and put the screws on Russia. You don't throw away so much, and gift your rival so much, if it isn't real. Ukraine not only has the anti tank missiles they desperately wanted, but a whole bunch of other aid trickling in rapidly, and most importantly, the military aid taps have probably been turned on permanently. They can probably buy almost whatever they want from the US/UK from now on. SAMs, aircraft, warships, etc, because why not? The genie's out of the bottle now, everyone now knows Russia could do the unthinkable.
Russia's entire foreign policy strategy is based on brinkmanship. That you never know what they're going to do next, how crazy they really are. If Russia backs down now, this policy is in ruins. Everyone will know that Russia will blink first if you just stand firm enough. I don't think the Russian government can take that.
B. That then kickstarts WW3
Nah. Nobody wants that. Russia would get its teeth kicked in by NATO and they know it. NATO doesn't want the casualties, the economic chaos, etc, or to find out what a cornered, defeated Russia might do next with the thousands of nuclear weapons it possesses. Nobody is bound by any alliance agreement to defend Ukraine, so they'll all just nope out of it. Even the UK and US.
The entire reason the UK is sending those missiles to Ukraine (aside from perhaps a smattering of genuine sympathy and affection for Ukraine) is so the UK doesn't have to fight a war. Best way to stay out of the conflict is give Ukrainians the weapons they need to fight it themselves. The UK and US will also be giving Ukraine all their military intelligence, advice, training and a mountain of other material support.
If Russia is smart, they'll back down. On paper Russia's armed forces are much stronger, but their troops are pure trash. Low morale, bitter, poorly equipped conscripts who'll desert in droves at the prospect of an offensive war against a determined enemy that was never a threat to their country and that many consider their brethren. Russia risks humiliation if Ukraine can push their army over a tipping point. War is unpredictable, but the loyalty and professionalism of the average Russian soldier is more unpredictable than the determination of proud, free people defending their homeland.
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