TOKYO (Reuters) - As Japan looks for a quick, resolute response to North Korea s growing missile threat, some defense policy makers in Tokyo say it may be time to reconsider non-nuclear pledges and invite U.S. nuclear weapons on to its soil. Japan, the only country to suffer nuclear attack, upholds three non-nuclear principles that commit it not to possess, manufacture or allow nuclear weapons on to its territory that were adopted five decades ago.  Perhaps it s time for our three principles to become two,  a senior defense policy maker told Reuters, suggesting nuclear weapons be allowed into Japan. He asked not to be identified because of the sensitivity of the issue. North Korea, pursuing its weapons programs in defiance of international condemnation, fired an intermediate ballistic missile over Japan last week, prompting authorities to sound sirens and advise residents to take cover. On Sunday, North Korea tested a nuclear device that had a  yield estimated at ten times that of the atom bomb dropped by the United States on Hiroshima in 1945. Inviting U.S. nuclear weapons would be an attempt by Japan jolt China, North Korea s sole major ally, to do more to rein in its neighbor by showing there are consequences to North Korean provocations that threaten its neighbors and destabilize the region, the policy maker said.  A simple way to do this could be for a nuclear-armed U.S. submarine to operate from one of the U.S. Navy bases in Japan, he said, a move bound to infuriate China. Former Japanese defense minister Shigeru Ishiba stoked controversy on Wednesday by questioning whether Japan can expect protection under the U.S. nuclear umbrella while maintaining its non-nuclear principles.  Is it right that we don t discuss this?  Ishiba asked in a television interview. In his election campaign last year, Donald Trump chided Japan and South Korea for not contributing enough to their defenses. On Tuesday, the president said he was ready to sell Seoul billions of dollars in weapons and scrap a limit on the size of warheads the Washington would supply.  We don t have any plan to begin discussing the three non-nuclear principles,  Japan Chief Cabinet Secretary Yoshihide Suga told reporters when asked to respond to Ishiba s comment.     Yet, the growing North Korean threat could stifle some of the opposition, experts say.  Just by raising this issue of nuclear principles, Japan will push the United States and China to act, and it is something that Beijing is not going to like,  said Takashi Kawakami, a security expert at Japan s Takushoku University.  It s the medicine that China needs to make it act against North Korea.  Allowing the U.S. military to deploy nuclear weapons on Japanese territory would pose a grave political risk for Prime Minister Shinzo Abe, particularly amid an influence-peddling scandal that has hit his popularity ratings. Any move toward relaxing the non-nuclear principles, however, is unlikely to lead to a home-made atomic bomb, despite Japan s technical abilities, say experts.  Tokyo has the civilian nuclear program, fissile materials and the weaponization technology necessary. It could probably develop a small arsenal of nuclear devices within a year if there was motivation to do so,  said Emily Chorley, a nuclear weapons expert at IHS Janes. But doing so would force Japan to renege on its non-proliferation commitments and could severely damage Washington s alliances and position of strength in Asia.  This would signal that the Japanese no longer have confidence in U.S. extended deterrence,  said a former senior U.S. military commander who asked not to be identified because he is not authorized to talk to the media.  That would essentially mean that they no longer have confidence in the alliance.    
Allowing nuclear weapons in Japan could defuse North Korean threat, say some policy makers