Assuming no gunpowder weapons or explosives and no uses of vehicles directly in battle (so you couldn’t just run over their horses with your tanks.)
The Soviets have a huge advantage in troops and had inner lines of communication and reconnaissance since railroads and trucks and airplanes still exist. On the other hand, the Mongols have much better cavalry. (Although the Soviets had plenty of cavalry as well.)
I’m guessing the Mongols slaughter the first few Soviet armies with Parthian shot until the Soviets learn how to arm everyone with a bow. Quantity of arrows has a quality all its own!
Without gunpowder or vehicles, the soviets are useless. How many tardises are involved?
Minus gunpowder and explosives, what exactly are the Russians supposed to have been fighting with? I’ll grant that my knowledge of Russian military is not wide, but I suspect that you’ve left them with knives and the occasional flame thrower. They would have no armor against anything the Mongols’ weapons, while the Mongols would be well defended against the knives and still have their projectile weapons.
You’re basically asking how much raw meat it takes to fight an armored force.
Soviets simply load airplanes with rocks and stone the shit out of the mongol horde.
You said planes and trains still exist.
On a re-read, I think that the OP might be trying to ask how long it would take the Russians to develop the manufacturing infrastructure to fight the Mongols on the Mongolian technology level (i.e. mass manufacturing of spears and bows and distributing them), or whether they’d be slaughtered before they could get to that point?
I have no answer.
Closed.
People. This is NOT the way to solve the problem. (although, it might help hasten the solution)
samclem, moderator.