http://en.wikipedia.org/wiki/Japanese_nuclear_weapon_program#Nuclear_Non-Proliferation_Treaty
In 1995 the Clinton administration pushed the Japanese government to endorse the indefinite extension of the NPT, but it opted for an ambiguous position on the issue. A former Japanese government official recalled, "We thought it was better for us not to declare that we will give up our nuclear option forever and ever". However, eventually pressure from Washington and other nations led to Japan's supporting the indefinite extension.[18]
