Japan allowed U.S. nuclear-armed warships to call at its ports without prior consultation in a secret agreement during Cold War negotiations leading to a revision to the Japan-U.S. Security Treaty in 1960, U.S. documents show.

The Japanese government has adamantly denied such a secret arrangement existed.

Takashi Shinobu, a professor emeritus at Nihon University in Tokyo and an expert on the history of Japan-U.S. diplomacy, analyzed more than 20 U.S. government documents obtained after 2004 from the U.S. National Archives and Records Administration and the National Security Archive, a U.S. nonprofit organization.

The records concern negotiations from 1958 and 1960, primarily between Foreign Minister Aiichiro Fujiyama and U.S. Ambassador to Japan Douglas MacArthur II.

In February 1958, Prime Minister Nobusuke Kishi told the Diet that Japan would not allow the United States to bring nuclear weapons into Japan or its territorial waters.

However, the United States wanted to ensure that its warships would be able to freely call at Japanese ports even after the security treaty was revised.

In September 1958, the U.S. State Department issued a directive to MacArthur about a prior consultation system that Japan and the United States would introduce as part of the revision.

While deployment of nuclear weapons on Japanese territory would be subject to prior consultation, MacArthur was told to confirm that nuclear-armed warships would be able to continue to enter Japanese territorial waters and arrive at ports without prior consultation.

In October 1958, MacArthur went to a meeting with Fujiyama that was also attended by Kishi.

Afterward, MacArthur reported to the State Department that he had explained the U.S. position to Fujiyama in accordance with the directive.

In April 1959, MacArthur reiterated to Fujiyama that the prior consultation system “will not be interpreted as affecting present procedures, which are working quite satisfactory, re deployment of U.S. forces and their equipment into Japan, including those for entry of U.S. military aircraft and entry into Japanese waters and ports by U.S. navy vessels,” according to a U.S. document obtained by Shinobu.

“Fujiyama said he accepted our understanding and perceived no difficulty,” the document said.

In May 1959, the State Department instructed MacArthur to prepare a classified document about the understanding between the two countries to “avoid any misunderstanding with subsequent Japanese governments,” according to another U.S. document.

However, Fujiyama balked at the U.S. proposal, presumably out of fear that such a document, if leaked, would deliver a serious blow to the government because it contradicted Kishi’s Diet statement.

In June 1959, Hisanari Yamada, vice foreign minister, told MacArthur that Fujiyama was considering the “possibility of having a classified interpretive understanding take the form of (a) ‘record of negotiations’ wherein each side would clearly set forth its position for (the) record,” according to a U.S. document.

MacArthur and Fujiyama eventually signed a “record of discussion” on the prior consultation system, dated Jan. 6, 1960.

Japan and the United States signed the revised security treaty on Jan. 19, 1960, but kept the record of discussion confidential.

Takuma Nakashima, a professor of Japanese political and diplomatic history, said the newly obtained documents shed valuable light on the background to Fujiyama agreeing to prepare the classified document on the understanding.

Nakashima said the issue relates to when Japan first formulated its non-nuclear policy and called on the Foreign Ministry to determine the facts of negotiations leading to the revised security treaty.

In 1981, Edwin Reischauer, who served as U.S. ambassador to Japan between 1961 and 1966, disclosed that there was an “understanding” on U.S. nuclear-armed warships calling at Japanese ports without prior consultation even before he became ambassador.

The Foreign Ministry investigated only related Japanese documents between 2009 and 2010, when the now-disbanded Democratic Party of Japan was in power.

It disclosed classified documents, including a copy of the record of discussion between Fujiyama and MacArthur.

But Foreign Ministry officials denied the existence of a secret agreement on nuclear-armed warships, saying there appeared to be disagreements in perceptions between the two countries.

While the record of discussion said the prior consultation system was “not interpreted as affecting present procedures,” Foreign Ministry officials said Japan did not think it meant that port calls by U.S. nuclear-armed warships would not require prior consultation.

The officials said Japan thought the phrase referred to general procedures about warships, such as exemption from harbor charges.

In 1967, Prime Minister Eisaku Sato announced Japan’s three non-nuclear principles of not possessing, not producing and not allowing the entry of nuclear weapons into the country.

The government has explained that nuclear-armed warships not only calling at Japanese ports but also passing Japanese territorial waters require prior consultation.

“It is not expected that nuclear-armed warships will call at ports because the United States is well aware of Japan’s three non-nuclear principles, in addition to the U.S. nuclear policy (of not equipping warships with tactical nuclear weapons) after the end of the Cold War,” Foreign Minister Yoshimasa Hayashi told the Diet in 2022.