In WWII Japan had to calculate the number of civilians in the US who were armed and how many might reinforce the army if they attempted an invasion. They ruled invasion out as a result.
Yes they did.
Adm. Yamamoto studied in America in the 1930's @ Harvard. He was the man who designed the surprise attack on Pearl Harbor.
Yamamoto was pragmatic and having lived in the US he did not have "rose colored leses" about US capabilities, our psyche, and our values. He knew a surprise attack would galvanize the US population, would enrage the US populace, and while it would (hopefully) smash the US Pacific fleet, that US industrial capacity would replace whatever was lost in short order.
(from what I have read, and this is from memory - so if I get something wrong speak up)
The idea was floated to invade the mainland US. Now, the exact details I don't know, but maybe it was to hold the US cities hostage, maybe toss in Hawaii too - but they knew they could not invade and hold onto US territory as a permanent possession.
They could however extort the US to stay out of the Pacific, and maybe even extort the oil, steel, and aluminum that the US had embargoed due to Japan having invaded China.
Yamamoto counseled against this. His famous quote was:
"You cannot invade mainland United States. There would be a rifle behind every blade of grass."
Of course the Japanese high command was horrified. But, not in the way you think: remember that in Japan only the Army and Samurai classes were allowed to have weapons. This was a long held tradition in Japan. The "peasants" were NOT allowed weapons. Such is why nun chucks and other "home made" weapons were invented. Nun Chucks were actually used for farming, and then later became weapons.
But, I digress.
The Japanese viewed the US freedom of privately owned weapons as an insane idea : after all theirs was an orderly and controlled society.
So - yes, the story is true - the US was not invaded because of the 2nd Amendment.
Those that scoff at this idea need to remember that Japan was a formidable world power with a battle hardened army, a seasoned navy with a good leadership. The US, while having a good industrial base, was largely an agrarian society with a small underfunded armed forces.
But, facing off against a country with a population with 130 million, of whom 20-40 million were armed was not something the Japanese wanted.
Oh, and to those who say the 2nd Amendment is silly in today's modern time - realize that Japan had aircraft carriers, radios, aircraft, machine guns, mortars, artillery, bombers, a well trained battle staff and a will to conduct a brutal form of warfare - and Japan analyzed the US mainland as a target, even a limited target for grabbing cities to ransom, and gave the operation a complete pass.
Hope this adds to the discussion.
Steven