East Asia Nuclear Policy Project
July 21, 1999
Japan Under the
US Nuclear Umbrella

Hans M. Kristensen

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Photo of USS Kitty Hawk
USS Kitty Hawk sailors spell out "Hajimemashite Nippon" ("Glad to meet you for the first time, Japan") on the flight deck of the carrier. U.S. Navy photo, 8/5/98.

Executive Summary

  • Introduction and Summary
  • The Early Years
  • The Battle over Okinawa 
  • The "Secret" Agreement
  • Nuclear War Planning in Japan
  • About the Author


  • Asahi Shimbun, August 25, 1999, p. 5. English evening edition. Available in HTML-format or PDF-format.
  • The Mainichi Newspapers, August 5, 1999, p. 8. English evening edition (PDF-format).
  • Asahi Shimbun, August 4, 1999, p. 4. Japanese morning edition (PDF-format).

  •   Japan Under the US Nuclear Umbrella (PDF-format)

  •    Freedom of Information Act Documents (PDF and HTML format)

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  • Executive Summary

    During the Cold War, rumors concerning U.S. deployments of nuclear weapons to Japan were both numerous and widely reported. Such rumors were consistently met with adamant denials by Japanese governments and a refusal by U.S. governments to discuss any aspects of nuclear weapons deployments overseas. Despite the end of the Cold War and the U.S. withdrawal of its last forward-deployed tactical nuclear weapons seven years ago, information about U.S. nuclear operations in Japan has remained shrouded in military secrecy.

    The Nautilus Institute's East Asia Nuclear Policy Project, a far-ranging project aimed at promoting open debate over the role of nuclear weapons in the Asia-Pacific region, has for the past year sponsored detailed research into the history of U.S. nuclear weapons practices in Japan. U.S. government documents recently declassified under the Freedom of Information Act and obtained through this research add substantial weight to previous assertions that the United States routinely brought nuclear weapons into Japan during the Cold War despite Japan's non-nuclear policy. These documents also shed light on suspicions that Japanese government officials knowingly accepted these deployments. Perhaps most surprisingly, the declassified documents also reveal the previously unreported extent to which the United States also conducted nuclear war planning in Japan.

    Nautilus Institute Research Associate Hans Kristensen has compiled these findings into a comprehensive, chronologically organized report that combines an array of previously unknown facts with news reports to portray clearly the extent to which the United States and Japan both allowed Japan to become involved in U.S. nuclear weapons practices. The following are the main findings and conclusions from the report.

    Deployment of Nuclear Weapons in Japan

    Allegations that the United States brought nuclear weapons into Japan despite the Japanese ban against nuclear weapons in its territory were frequent during the Cold War. Such allegations were always denied by Japanese governments. The newly declassified documents obtained for this report, however, provide important new reinforcement to these allegations. Indeed, references in these documents to U.S. nuclear weapon operations on Japanese soil and through Japanese harbors and territorial waters are commonplace. The strength of this evidence leaves little basis to continued insistence that the United States ever respected Japan's three non-nuclear principles.

    In particular, the newly declassified documents disclose the following:

    1. In 1972, during preparations to establish Yokosuka as the home port of the USS Midway (CV-41) the following year, the U.S. State Department recommended removing nuclear weapons from the aircraft carrier to avoid a conflict with Japan's non-nuclear policy. The Chief of Naval Operations, however, vetoed this move as "operationally unacceptable." Yokosuka subsequently served as the home port for the Midway for two decades.

    2. During the 1970s and 1980s, special nuclear weapons training and nuclear weapons handling procedures existed for the USS Midway (CV-41). These special procedures, unique to this vessel, enabled nuclear weapons to be removed from the vessel outside Japanese territory. This capability apparently implemented an unwritten agreement under which Japan would permit the United States to bring nuclear weapons into Japanese ports as long as the United States did not remove offload them to shore.

    3. Shortly after a visit to Yokosuka in October 1979, the aircraft carrier USS Kitty Hawk (CV-63) was dispatched to the East China Sea to defend against a possible North Korean aggression against South Korea during the chaotic period following the assassination of President Park Chung-hee. During this deployment, the ship conducted both nuclear anti-submarine and nuclear strike exercises. Such exercises during such a crisis situation would be highly unlikely unless the ship was carrying nuclear weapons, strongly suggesting that the ship was nuclear armed during its preceding visit to Japan.

    4. Contingency plans existed in 1967 for deployment of the Genie air-to-air missile to Japan. Although the Genie missile is dual-capable, the documents clearly identify the missiles that would be deployed under these contingencies as nuclear missiles. This represents the first association of nuclear-armed Genie missiles with Japanese deployment. The details of the contingencies under which the missiles would be deployed remain classified.

    5. The Japan Air Self Defense Force conducted joint air defense exercises with U.S. forces in 1962 that included practicing procedures for transmitting nuclear weapons launch authorizations as part of the Single Integrated Operational Plan (SIOP). Whether the Japanese forces participated directly in practicing these procedures is unknown.

    6. With the reversion of Okinawa to Japanese sovereignty in 1972, Japan stated that all nuclear weapons related functions on the island must cease. Despite this position, U.S. forces on Okinawa were maintained on nuclear alert as part of the SIOP for several years after the reversion of the island, and some forces even increased their nuclear alert role in the 1970s.

    7. Although nuclear weapons were removed from Okinawa in the early 1970s, this was not simply in response to the conditions for reverting the island to Japanese sovereignty, but was undertaken as part of a much larger U.S. withdrawal of forward-deployed tactical nuclear weapons from East Asia in response to increasing concerns over the vulnerability of these weapons to terrorist attacks. (The newly declassified documents confirm for the first time that U.S. land-based nuclear weapons were removed from Taiwan and the Philippines in 1974 and 1976, respectively, although naval nuclear weapons subsequently continued to enter both countries aboard warships. Previous Nautilus Institute research has provided the first official account of how nuclear weapons were removed from South Korea in 1991.)

    8. At about the time of the reversion of Okinawa to Japan in 1972, both the Commander in Chief of the U.S. Pacific Command (CINCPAC) and the U.S. National Security Council (NSC) concluded that the Japanese government "tacitly" permitted nuclear weapons to enter Japanese harbors onboard warships. (Note the relevance of this finding to those outlined in the following section)

    Each of the new revelations above is described and supported in detail in the report.

    "Secret" Agreements

    In addition to the question of whether the United States deployed nuclear weapons and conducted nuclear operations in Japan throughout the Cold War, there have also been frequent allegations among analysts and in news media that U.S. and Japanese governments made one or more "secret agreements" allowing nuclear weapons to enter Japan despite the country's official nuclear ban. The most widely reported of these allegations is that the United States and Japan, in connection with negotiation of the 1960 Treaty of Mutual Cooperation and Security, reached a secret unwritten understanding to permit U.S. warships to carry nuclear weapons in Japanese territorial waters.

    The newly declassified documents obtained for this report provide ample evidence that Japanese governments willingly overlooked indications that its non-nuclear principles were violated. The declassified material also confirms that the U.S. government and military authorities had concluded that Japanese governments tacitly allowed nuclear weapons to be onboard U.S. warships in Japanese ports. In some instances, Japanese officials were present onboard U.S. aircraft carriers to witness conspicuous displays of practice exercises for use of nuclear weapons. The newly declassified documentation even reveals instances in which Japanese government officials urged the United States to conceal the armament of the nuclear ships.

    Nowhere is the Japanese willful disregard of U.S. nuclear weapons practices in Japan more evident than in the case of the Ticonderoga scandal in 1989, which erupted after independent researchers obtained copies of official U.S. Navy documents revealing that in 1965 the aircraft carrier USS Ticonderoga (CV-14) carried nuclear weapons into Japan. The report shows how the Japanese government simply decided to ignore the weight of the evidence and ride out the storm of public criticism.

    The report's analysis of the newly declassified documents shows how Japan's quiet acquiescence to US nuclear weapons practices in Japan was an indirect result of the culture of secrecy created by the U.S. policy to "neither confirm nor deny" (NCND) any deployment of nuclear weapons. The inauguration of the NCND policy coincided with Japan's early (but unsuccessful) efforts in the late-1950s to elicit U.S. assurances that it would not introduce nuclear weapons into Japan. Although the United States said many times that it respected its security treaty and associated arrangements Japan, the United States never stated explicitly that it respected Japan's non-nuclear policy. Japan's acceptance of application of the NCND policy to Japanese ports enabled the United States to avoid falsely denying its nuclear operations in Japan. Thus, Japanese governments consistently exercised a contradictory, if not hypocritical, attitude toward U.S. nuclear weapons practices. In public, Japanese governments stood by the nuclear ban devoutly, and reiterated it each time the government was confronted with evidence of a violation. In private, however, governments maintained a more pro-nuclear disposition epitomized by tacit acceptance of the nuclear ambiguity demanded by the NCND policy.

    The coexistence of these two contradictory positions imposed a burden on Japanese policymakers and created a tension in U.S.-Japan security relations whose diplomatic consequences resonate even to this day. Although the arrangement accommodated conflicting political and security imperatives of the day, its perpetuation has damaged the credibility of the U.S.-Japan military alliance among the Japanese public. The U.S. government, like the public in general, was aware of the dilemma imposed on Japanese governments each time a ship visit occurred. However, the United States continued to insist on complete secrecy concerning its nuclear weapons practices, leaving Japanese authorities to deal with the political fallout. Forced to choose between ignoring its own nuclear ban or confronting its most important ally, for nearly five decades Japanese governments have sacrificed their own non-nuclear policy.

    U.S. Nuclear War Planning In Japan

    In addition to further verifying both the presence of U.S. nuclear weapons in Japan and official Japanese acquiescence to this presence, the newly declassified documents obtained for this report reveal for the first time that the United States also conducted nuclear war planning in Japan.

    Specifically, seven years after Japan and the United States signed the 1960 Treaty of Mutual Cooperation and Security, the Commander of the Pacific Command established the Pacific Operations Liaison Office (POLO) in Fifth Air Force facilities at Fuchu Air Station just outside Tokyo. POLO functioned as the liaison office for U.S. nuclear operations in the Western Pacific area from the mid-1960s until July 1972. During this period, POLO was responsible for the production of the Reconnaissance Plan portion of the Single Integrated Operational Plan (SIOP) for the Pacific Command (PACOM), as well as various other nuclear planning documents.

    By 1972, modernization of the SIOP planning process allowed Pacific Command to move the POLO function to Hawaii as part of an overall consolidation of SIOP planning. However, SIOP functions continued to take place on Japanese territory. For example, the Yokota and Kadena Air Bases in 1965 were designated as dispersal bases for U.S. Strategic Air Command's new airborne command post aircraft, codenamed BLUE EAGLE. Together with the U.S. Navy's own specially equipped C-130 aircraft, these command and control aircraft operations out of Japan functioned to provide the National Command Authority (the President, the Secretary of Defense, the Chairman of the Joint Chiefs of Staff and other high-ranking military officials) with the technical means of authorizing and controlling SIOP and Theater nuclear war plans in the region. During the 1970s, BLUE EAGLE aircraft flying out of Japan practiced transferring nuclear launch orders to strategic nuclear submarines and nuclear-armed aircraft carriers operating in the waters around Japan. Such nuclear command and control exercises continued well into the 1990s, and probably continue even today.

    Unlike a visit of a nuclear-armed aircraft carrier, nuclear war planning and nuclear command and control exercises in Japan are much less visible to the public. Because of its relative ease of concealment, this aspect of Japanese involvement in U.S. nuclear weapons practices has received scant public scrutiny. The new evidence described in this report of the use of Japanese facilities for nuclear war planning therefore reveals the depths to which a non-nuclear country can find itself involved in nuclear arms rivalries -- whether it is aware of it or not -- by accepting the security guarantees of a nuclear-armed ally.

    Post Cold War Relevance

    The evidence from the newly declassified documents used to generate this report points clearly to the conclusion that Japanese governments lied to the public when they insisted they had no reason to suspect that the United States was violating Japan's non-nuclear policy. The material upon which this report is based clearly shows that Japanese governments had sufficient information about U.S. nuclear weapons practices to allow them to act. Throughout the Cold War, Japanese governments chose not to act on this knowledge.

    The legacy of Cold War era U.S.-Japanese nuclear relations provides important lessons about the long-term consequences of sustained concealment of the underlying realities of security alliances. Regardless of the military rationale used at the time to justify the deployment of nuclear weapons in Japan, the secrecy and denials that accompanied the deployments created a political legacy that endures to this day. In the context of the current strengthening of the U.S.-Japan military alliance (as exemplified by the recent adoption of the new U.S.-Japan guidelines for security cooperation), careful examination of this legacy becomes all the more vital. A complete and accurate accounting of history is necessary to salve the irritation of this legacy of secrecy, which could contribute to a future public backlash against the U.S. military presence in Japan. It is also a prerequisite to removing the opacity that continues to shroud the true nature of the present and planned security relationship between these two countries.

    Now that U.S. nuclear weapons have been withdrawn from the Pacific, the opportunity exists for both Japan and the United States to revisit the premises of their security relationship, and especially to critically examine whether a Cold War-level reliance upon nuclear deterrence remains an effective means of achieving their mutual security goals. This imperative applies particularly to Japan, which publicly espouses nuclear disarmament, but also continues to accept the prospect of future U.S. transit of nuclear weapons through Japan and allows the United States to conduct routine nuclear command and control operations from its territory.

    A vital step toward such an examination of the future role of nuclear deterrence in the U.S.-Japan relationship would be for the Japanese government to provide greater access to its own information on the past. Ironically, most of the new information presented in this report comes not from Japan but from the United States -- the country that brought nuclear weapons into Japan. Information from the Japanese government's archives, on the other hand, is virtually unavailable and represents an important "missing link" in fully understanding the nuclear relationship that evolved between the two countries during the Cold War. With the Cold War now over, many justifications for maintaining this secrecy have evaporated. Japan now has the opportunity to allow drastically increased public access to this historical material. By doing so, it would help close the gaps in the history books, dispel rumors and myths, and facilitate a more open public debate on both sides of the Pacific about what the proper nature of the U.S.-Japanese military alliance should be.


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