I have blogged about Japan and nuclear weapons in the past. Japan is the only country on Earth to have suffered nuclear attacks. The dropping of the atomic bombs on Hiroshima and Nagasaki on Japan helped to bring World War II to an end in the Pacific. The post-World War II Japanese Constitution forbids the development of nuclear weapons by Japan. There are factions in Japan who would like to see that prohibition struck from the Constitution. The Major General of the Japanese Self-Defense Force has called for altering Japan's policy on nuclear weapons. The new Prime Minister of Japan has stated that Japan would "revise its pacifist constitution, which limits its military activities to self-defense."
Several small islands north of Taiwan, referred to collectively as the Senkaku Islands, were controlled by the Japanese from 1895 until 1945. Following the end of World War II in the Pacific and the surrender of Japan, the United States administered the uninhabited islands from 1945 to 1972 when they returned control of the islands to Japan. China argues that the islands were seized by the Japanese and should have been returned to Chinese control as many conquests of Imperial Japan were returned to other nations in 1945. These islands are included in a defense treaty between Japan and the U.S. If they are seized by another country, the U.S. would be bound by the treaty to intervene on Japan's behalf.
In November of 2013, China announced the East China Sea Air Defense Identification Zone which included the Senkaku islands. China said that any aircraft flying over the islands would have to file a flight plan and submit information about transponders on the aircraft. Japan and the U.S. objected strongly to the Chinese announcement and said that they would not honor China's demands.
Asia Weekly, a Hong Kong-based newspaper has recently reported that the Japanese are secretly developing a nuclear weapons capability because of the increasing tensions between China and Japan with respect to the Senkaku Islands in the East China Sea. The Chinese are especially upset about Japan's reluctance to return a third of a ton of weapons-grade plutonium to the United States. The plutonium was given to Japan for research purposes in the 1960s. However, this is a tiny amount compared to the forty tons of plutonium that Japan possesses.
Japan is heavily invested in nuclear technology and hopes to revitalize its economy by exporting nuclear reactors to other countries. The Asia Weekly claims that Mitsubishi, Hitachi and Toshiba along with two hundred smaller member of the Japanese nuclear industry possess all the expertise necessary to rapidly develop nuclear weapons if called upon by the Japanese government.
China has been increasingly belligerent in public pronouncements lately. They said that they could easily destroy the U.S. fleet in the Pacific. They published maps of the U.S. cities that they said they could destroy in a nuclear strike. They sunk a fake U.S. carrier with a new type of missile and bragged about it. Whatever the Japanese interest in developing nuclear weapons, China's recent provocative statements give the Japanese every reason to be concerned about possible future conflicts with China. If the Japanese do develop nuclear weapons, the Chinese will be a large part of the reason.
