This story is ridiculous on so many levels it ranks with those kidney theft emails that were circulating a few years ago. Whoever wrote it clearly knows nothing about Japanese intentions towards the USA during WWII. As for the population being armed and dangerous, I'm sure the Russians had just as many hunting rifles as the USA circa 1942 and did it stop the German Blitzkrieg?
But why listen to me? Here are some facts about a proposed Japanese invasion of Australia and why it was rejected. Multiply that by a factor of 10 and you'll see why an invasion of the USA was never in the cards.
http://tinyurl.com/oz6ay5
The way I see it, the only reason Americans need guns is to protect themselves from other Americans with guns. Of course they'll make up stories (like this one) to justify their position, but the bottom line is Americans are simply afraid of each other.
ebear