I can offer a really useful and detailed response for classic (2nd ed.), but I haven’t played First Edition. Are the two similar enough that a 2nd edition example would be helpful?
What is so bad about taking Karelia in the first turn(s)?
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I would probably suggest going against building an IC in Yakrut for Japan. It’s much more economical to just buy two transports instead. Usually when I set up an IC (India or Burma, maybe for both), it’s to produce ARM and not inf. I think that 6 ARM should be more than enough (if you factor in supporting inf) per Japan once it hits critical mass.