The last mission is painfully easy thanks due to crappy base design. it's possible to beat it without the need of the Chronosphere, the Weather machine or basically any tank/armor weapon.
What to do:
First off if you arn't quick enough, then when you build your base build your war factory in the top left, away from all your other buildings. When the Soviets launch nukes your war factory is awlays targeted first. Then all you need to do is set up some prism towers at your entrances and make sure you don't lose any of the oil derricks. Next build the Spy Satellite, that is needed. With that out of the way, build as many chrono Legionnaire as possible. They are built at your barracks, and require a battle Lab. Once you have like 4-6 of them, grab 4 and teleport them to the bottom left of the main base of the Sovets. two should be teleported to the far right side with the two nuclear power plants. There is enough room where the Tesla coil will not touch them, and if placed right the Apocalypse tank won't move to intercept them. even if it does, it will only get off around 3 shots, which will put one Legionnaire into red. Thats it. Once you have your Legionnaire in the soviet base, proceed to wipe out the four power plants on the bottom, and the two on the far right side of the map. With them out of the way, the Nuke and Iron Curtain are disabled, and so are all the automated defense. From here its a simple matter of removing the couple buildings around the Kremlin for an easy win.
Par time is around 2 hours, you can get it done in around 30 minutes