However, the question is; "Can the US enter the Soviet Union via the Soviet Far East with ground troops on transports and/or air units flying in once it is; (1) at war with Japan and (2) the Soviets and Japanese are not at war yet, therefore still under the non-aggressive pact treaty?
I don’t know if there are any rule about it, but if we were playing a game together and the issue shows up, I would argue the following:
US Troops can enter the USSR via de Far East, as long as they are not engaged in any hostile activity against Japanese forces.
i.e.: if for some odd reason the USA wants to reinforce the USSR via the Far East, in order to get to Europe from there (long walk from Siberia to Moscow though), well, that’s ok.
But, if the US is trying to use Soviet territory as a base to attack Japan, that would be read by Japan as an act of war from the USSR. So I would say that the USSR is declaring war against Japan by doing so.
in both cases, the USSR would loose her NO’s additional IPC