To be realistic Ivan is probably more worried about China and Iran than us.
The Chinese have been eyeing Siberia for decades and the Russians know it. Lots of resources there that could truly make China an independent country. Much like the Japanese lashed out before and during WWII because of their lack of raw materials, the Chinese are feeling the same.
In 1969, has a newly minted tank commander out of the NCOCC at the Armor School, we were familiarized with the use of the 90 mm main gun on the M48A3 in the indirect fire role, using a gunner’s quadrant and the gunner’s azimuth indicator. We had aiming stakes and took directions from an improvised Fire Direction Center, with firing tables for the 90 mm M17A1 HE round, the fuse of which could be set for point or delayed detonation.
I believe the maximum ordinate would yield a maximum effective range of 16,000 meters or so.
We were told that this was an inefficient use of tank guns, due to the relatively small bursting radius of the 90mm HE round and the accelerated wear on the gun tube, but could be employed in an emergency.
I wish Ivan was worried more about Iran instead of teaming up with them in Syria!