Oh, absolutely.... the Japanese could probably do it almost overnight. They certainly have the engineering know-how, and the recent suppression of the old warrior ethic is just that- a fine patina laid over a very hard core. The iron is still there....
Ah, the lessons we can learn from history (by those who bother with doing some reading.) How few under age 60 really have bothered to look at what the Japanese did during W W II.
Not only is China a threat to Japan but North Korea fired a missle "accidently" right over Japan in the recent past. Let the Japanese stare the North Koreans down with a nuke threat. As you said, "The iron is still there."