On March 18, 1975, in a show of defiance against Japan-U.S. military policy, the Kobe Municipal Assembly passed a resolution that became known as the "Kobe Formula."
From that day forward, the resolution said, any ship carrying nuclear weapons would not be allowed to enter Kobe harbor, and would have to officially declare it did not have any nukes on board. French, Indian and Italian naval vessels agreed to cooperate, but the U.S. Navy refused.
In the nearly four decades since, there has been little pressure on the part of the United States to change it. Following the Great Kobe Earthquake of January 1995, the U.S. offered to dispatch its navy to Kobe for humanitarian assistance. Partially due to the Kobe resolution, the various offers were mostly declined.