close, but you've hit something important tak, it fits in every clue but instead of being invaded by a third country it was invaded by USA itself. I cannot say the reason is because of American Submarines passing by, but if they didn't they sure wanted to :p
I'm trying to help you all: What is the communist arch-enemy of USA? Where was this arch-enemy? Where do US Subs want to pass through? US Subs are in the Atlantic and the Pacific, what is the other ocean that they are not there and need a passage?
As i said NHL's Fiji were close, tak's Vietnam was also close, i would bet somewhere in the middle :p