Nuclear sharing is not a shortcut to deterrence
IWAMA Yoko / Professor, National Graduate Institute for Policy Studies
August 19, 2022
Since the Russian invasion of Ukraine, some in Japan have argued that Ukraine could not deter the Russian invasion because it had no nuclear weapons. If Japan were to deter such an invasion, the argument goes, it should at least think about “nuclear sharing” with the US as is the case with some NATO member countries, even though it would be unable to possess nuclear weapons. This argument contains some misconceptions about “nuclear sharing”.
Firstly, nuclear ‘sharing’ does not mean ‘possessing’ nuclear weapons. The nuclear weapons belong only to the US, and the term ‘sharing’ is used insofar as the participating countries would be involved in the operation of the use of the weapons in wartime. 5 NATO member countries, i.e. Germany, Italy, Belgium, the Netherlands, and Turkey participate in nuclear sharing with the US. In Germany, tactical nuclear weapons for use on a battlefield (small US nuclear weapons called B61) are stockpiled in a German Bundeswehr base under strict US custody. The arrangement is that, once war starts and NATO decides to use these weapons, the US military would provide these weapons to the Bundeswehr for use by the Bundeswehr on board its fighter aircraft, the so-called DCAs (Dual Capable Aircraft: meaning capable of carrying both conventional and nuclear weapons). There are estimated to be a total of 100 B61s in those five countries.
During the Cold War era, NATO had the basic defense strategy of using tactical nuclear weapons in an emergency against the invasion by the Soviet ground forces which were believed to possess superior conventional capabilities, and many nuclear weapons were deployed in West Germany and elsewhere. France, for its part, asked the question of whether the US would use its nuclear weapons to defend Paris and, believing that the US would likely sacrifice Paris to defend New York, decided to develop its own nuclear weapons. As similar doubts were raised among the NATO allies in Europe, the US feared that West Germany and others might join the skeptics. This gave rise to the idea of operating the US nuclear weapons together. Those countries joining the nuclear sharing scheme entered into bilateral arrangements with the US, and the scheme as a whole took its present shape within the NATO framework by the end of the 1960s.
At its peak in the 1970s, there were more than 7,000 American nuclear weapons in Europe, which have subsequently been reduced. One may ask whether 100 small nuclear weapons in Europe would have any military significance. I see this more as a symbol of American political commitment than a real military asset. For both the US and the Soviet Union during the Cold War era, it was vitally important in terms of security and geopolitics that Germany, which had sparked World War II and was split into the East and West as a result of its defeat, would never possess nuclear weapons. Nuclear sharing was the compromise finally arrived at as a result of a decade of painstaking groping by the US, its allies, and the Soviet Union for ways to achieve this.
Secondly, nuclear sharing is a part of the system designed to maintain the credibility of the US’s extended nuclear deterrence among its allies and to prevent the proliferation of nuclear weapons. NATO has the framework for consultation called the NPG (Nuclear Planning Group) comprising its 29 member countries except for France. The nuclear weapons that are shared under the nuclear sharing scheme cannot be used without consultation and approval by the NPG. The NPG also shares among its member countries information not only on the operation of nuclear weapons but also on nuclear policies in general, thus enhancing the credibility of nuclear deterrence. It is also closely tied into the NPT (Nuclear Non-proliferation Treaty) regime since the custody of the nuclear weapons in peacetime is strictly under US hands.
Thirdly, even under the scheme of nuclear sharing, a participating country cannot make at its will the very grave decision of using nuclear weapons. However small a nuclear weapon may be, once it is used, it can trigger the process of escalation. The possibility of total nuclear war cannot be ruled out. Under such an arrangement, even if Japan wanted to use nuclear weapons to defend its national interest, it is inconceivable that the US would easily go along. Conversely, in a situation where the US decides to use nuclear weapons, if Japan refuses to go along, it can lead to the collapse of the Japan-US security alliance. The custody of American warheads in Japan, even under American control, would be against the ‘Three Non-nuclear Principles.” For Japan to possess its own nuclear weapons would be against the NPT. Whether nuclear sharing would be welcome under the current NPT regime is questionable to say the least.
There is too much of a leap in logic to talk about nuclear sharing concerning Japan today. The reasons are as follows.
While Europe has focused on how to deal with the threat of ground forces since the Cold War era, Japan is surrounded by sea and faces the problem of deficiencies in Japanese and American long-range strike capabilities such as cruise missiles with conventional warheads and ballistic missiles. We should first think about strengthening these capabilities. Are we to strike the invading warships and fighter aircraft one by one? How close to Japan should they come before we strike? Should we possess conventional weapons with long-range strike capabilities to destroy the port facilities and airfield runways of the invading country so that we can forestall these attacks in advance? As the debate on “enemy base strike capability” takes place in the Diet, there should be a serious national debate on these issues.
Nuclear weapons would not function as a deterrent without the resolve to use them eventually. Would the Japanese people support the decision to use nuclear weapons militarily? Putin invaded Ukraine because he was convinced that the US would never use nuclear weapons in a situation like this, nor would the US intervene militarily. Total nuclear war is an option that no rational leader can ever take. This said, the leader of any country could drive himself over the edge when pushed to the limit. Should this ever happen with nuclear weapons, that would spell an unprecedented catastrophe for humankind. Even under a nuclear sharing arrangement, it would be the Japanese prime minister who orders the Self Defense Force to use a nuclear weapon. I urge people to ponder the historical implications of such a decision. Japan’s human and economic resources should be used for purposes other than nuclear sharing.
The relationship of trust which makes the US nuclear umbrella work when the need arises and enables the US to help Japan when Japan needs help is the essence of the deterrence provided under the Japan-US alliance. For this to work, there should be even closer consultations than before on military operations among Japan and the US and their neighboring partners such as Australia and the Republic of Korea. Japan should demand that the US engage in consultations similar to those with the NATO allies, and establish a new system to that end if necessary. Even without nuclear sharing, such consultations can take place. In fact, they should take place. Japan has been negligent about discussing a variety of options that constitute the overall deterrence in the early stages of the war. The lack of these options will weaken the entire deterrence leading to the ultimate phase of nuclear war. In particular, should there be contingencies in Taiwan Strait or the Korean Peninsula, we would have to be prepared with a broad range of options including the evacuation of Japanese nationals.
If we possess something that we cannot use, the satisfaction that we derive from will be nothing more than an illusion. Even if it takes money and time, we should
keep making steady and painstaking efforts in all kinds of preparations for defense. Nuclear sharing is not a shortcut to deterrence, and there is no shortcut to deterrence.
Yoko Iwama is a professor of international relations at the National Graduate Institute for Policy Studies.
Firstly, nuclear ‘sharing’ does not mean ‘possessing’ nuclear weapons. The nuclear weapons belong only to the US, and the term ‘sharing’ is used insofar as the participating countries would be involved in the operation of the use of the weapons in wartime. 5 NATO member countries, i.e. Germany, Italy, Belgium, the Netherlands, and Turkey participate in nuclear sharing with the US. In Germany, tactical nuclear weapons for use on a battlefield (small US nuclear weapons called B61) are stockpiled in a German Bundeswehr base under strict US custody. The arrangement is that, once war starts and NATO decides to use these weapons, the US military would provide these weapons to the Bundeswehr for use by the Bundeswehr on board its fighter aircraft, the so-called DCAs (Dual Capable Aircraft: meaning capable of carrying both conventional and nuclear weapons). There are estimated to be a total of 100 B61s in those five countries.
During the Cold War era, NATO had the basic defense strategy of using tactical nuclear weapons in an emergency against the invasion by the Soviet ground forces which were believed to possess superior conventional capabilities, and many nuclear weapons were deployed in West Germany and elsewhere. France, for its part, asked the question of whether the US would use its nuclear weapons to defend Paris and, believing that the US would likely sacrifice Paris to defend New York, decided to develop its own nuclear weapons. As similar doubts were raised among the NATO allies in Europe, the US feared that West Germany and others might join the skeptics. This gave rise to the idea of operating the US nuclear weapons together. Those countries joining the nuclear sharing scheme entered into bilateral arrangements with the US, and the scheme as a whole took its present shape within the NATO framework by the end of the 1960s.
At its peak in the 1970s, there were more than 7,000 American nuclear weapons in Europe, which have subsequently been reduced. One may ask whether 100 small nuclear weapons in Europe would have any military significance. I see this more as a symbol of American political commitment than a real military asset. For both the US and the Soviet Union during the Cold War era, it was vitally important in terms of security and geopolitics that Germany, which had sparked World War II and was split into the East and West as a result of its defeat, would never possess nuclear weapons. Nuclear sharing was the compromise finally arrived at as a result of a decade of painstaking groping by the US, its allies, and the Soviet Union for ways to achieve this.
Secondly, nuclear sharing is a part of the system designed to maintain the credibility of the US’s extended nuclear deterrence among its allies and to prevent the proliferation of nuclear weapons. NATO has the framework for consultation called the NPG (Nuclear Planning Group) comprising its 29 member countries except for France. The nuclear weapons that are shared under the nuclear sharing scheme cannot be used without consultation and approval by the NPG. The NPG also shares among its member countries information not only on the operation of nuclear weapons but also on nuclear policies in general, thus enhancing the credibility of nuclear deterrence. It is also closely tied into the NPT (Nuclear Non-proliferation Treaty) regime since the custody of the nuclear weapons in peacetime is strictly under US hands.
Thirdly, even under the scheme of nuclear sharing, a participating country cannot make at its will the very grave decision of using nuclear weapons. However small a nuclear weapon may be, once it is used, it can trigger the process of escalation. The possibility of total nuclear war cannot be ruled out. Under such an arrangement, even if Japan wanted to use nuclear weapons to defend its national interest, it is inconceivable that the US would easily go along. Conversely, in a situation where the US decides to use nuclear weapons, if Japan refuses to go along, it can lead to the collapse of the Japan-US security alliance. The custody of American warheads in Japan, even under American control, would be against the ‘Three Non-nuclear Principles.” For Japan to possess its own nuclear weapons would be against the NPT. Whether nuclear sharing would be welcome under the current NPT regime is questionable to say the least.
There is too much of a leap in logic to talk about nuclear sharing concerning Japan today. The reasons are as follows.
While Europe has focused on how to deal with the threat of ground forces since the Cold War era, Japan is surrounded by sea and faces the problem of deficiencies in Japanese and American long-range strike capabilities such as cruise missiles with conventional warheads and ballistic missiles. We should first think about strengthening these capabilities. Are we to strike the invading warships and fighter aircraft one by one? How close to Japan should they come before we strike? Should we possess conventional weapons with long-range strike capabilities to destroy the port facilities and airfield runways of the invading country so that we can forestall these attacks in advance? As the debate on “enemy base strike capability” takes place in the Diet, there should be a serious national debate on these issues.
Nuclear weapons would not function as a deterrent without the resolve to use them eventually. Would the Japanese people support the decision to use nuclear weapons militarily? Putin invaded Ukraine because he was convinced that the US would never use nuclear weapons in a situation like this, nor would the US intervene militarily. Total nuclear war is an option that no rational leader can ever take. This said, the leader of any country could drive himself over the edge when pushed to the limit. Should this ever happen with nuclear weapons, that would spell an unprecedented catastrophe for humankind. Even under a nuclear sharing arrangement, it would be the Japanese prime minister who orders the Self Defense Force to use a nuclear weapon. I urge people to ponder the historical implications of such a decision. Japan’s human and economic resources should be used for purposes other than nuclear sharing.
The relationship of trust which makes the US nuclear umbrella work when the need arises and enables the US to help Japan when Japan needs help is the essence of the deterrence provided under the Japan-US alliance. For this to work, there should be even closer consultations than before on military operations among Japan and the US and their neighboring partners such as Australia and the Republic of Korea. Japan should demand that the US engage in consultations similar to those with the NATO allies, and establish a new system to that end if necessary. Even without nuclear sharing, such consultations can take place. In fact, they should take place. Japan has been negligent about discussing a variety of options that constitute the overall deterrence in the early stages of the war. The lack of these options will weaken the entire deterrence leading to the ultimate phase of nuclear war. In particular, should there be contingencies in Taiwan Strait or the Korean Peninsula, we would have to be prepared with a broad range of options including the evacuation of Japanese nationals.
If we possess something that we cannot use, the satisfaction that we derive from will be nothing more than an illusion. Even if it takes money and time, we should
keep making steady and painstaking efforts in all kinds of preparations for defense. Nuclear sharing is not a shortcut to deterrence, and there is no shortcut to deterrence.
Yoko Iwama is a professor of international relations at the National Graduate Institute for Policy Studies.
The English-Speaking Union of Japan
核共有は抑止力の近道ではない
岩間 陽子 / 政策研究大学院大学教授
2022年 8月 19日
ロシアのウクライナ侵攻以降、日本国内で、ウクライナは核兵器を保有していなかったが故にロシアの侵攻を抑止し得なかった、日本も侵攻されるのを抑止するために核兵器の保有はできないとしても、せめてN A T O加盟国のように米国との「核共有」を考えるべきだと議論が行われている。このような議論は「核共有」についてのいくつかの誤解を含んでいる。
第１に、核「共有」と言っても核兵器「保有」を意味するものではない。核兵器はacticalあくまで米国のもので、戦争で使う際に参加国が関与するので、運用全体に参加するという限りにおいて「シェア」と言われる。米国の核共有には、ドイ ツ、イタリア、ベルギー、オランダ、トルコの5N A T O加盟国が参加しており、ドイツでは、戦場単位の使用を想定した戦術核（B61という米軍の小型核兵器）を、ドイツ連邦軍の軍事基地の中で厳しい米軍の管理の下に保管しており、有事になれば、米軍がドイツ連邦軍に供与し、ドイツ連邦軍が自らの戦闘機（通常兵器と核兵器の双方を運用可能という意味で、「dual-capable aircraft（DCA）」と呼ばれる）に搭載して使用する約束となっている。この5カ国に計約100発のB61があると推定されている。
NATOは冷戦期、有事の際には通常兵器で優位に立つソ連側 地上軍の侵攻に対して戦術核兵器を投入する防衛戦略を基本としており、多くの核兵器が⻄ドイツ等に配備されていた。他方、フランスは「パリのために米国が核兵器を使ってくれるの か? ニューヨークを守るためには、米国はむしろパリを犠牲にするだろう」と考え、独自に核兵器を持つことを決めた。同様の疑念が欧州のNATO加盟国側で高まり、⻄ドイツ等が同調することを米国が恐れたため、米国の核兵器を一緒に運用する案が生まれた。核共有に参加する国が米国と2国間で取り決めを交わし、 1960年代末には全体のかたちがまとまった。
70年代のピーク時には欧州には7000発以上米国核兵器があり、それを削減してきたことを考えると、小型の核兵器が欧州に100発あることに果たして軍事的な意味はあるのだろうか？筆者はこれを実際の軍事的意味よりも米国の政治的コミットメントとして捉えている。 冷戦下の米ソにとって、第二次世界大戦の火種となり敗戦で東⻄に分裂したドイツが核を保有しないことが、安全保障上も地政学的にも重要だった。それを実現するために米国と同盟国、さらにはソ連が１０年間に渡り模索してたどり着いたぎりぎりの妥協が核共有であった。
第２に、核共有とは、米国の拡大抑止の同盟内の信頼性を維持し、かつ核拡散を防止するための制度である。NATOにはフランスを除く29加盟国が参加するNPG(核計画グループ)という協議の枠組みがあり、核共有されている核兵器はここで協議して承認されなければ使うことはできない。また、NPGでは、核の運用に限らず核政策全体についても参加国内で情報をシェアすることで核抑止力の信頼性を高めている。また、平時における核兵器の管理は厳格に米軍により行われるので、N P T（核拡散防止条約）体制にも密接に組み込まれている。
第３に、たとえ核共有をしても、その極めて重たい決断を参加国が勝手に下すことはあり得ない。どんなに小さくても核兵器を使うと、そこから核のエスカレーションが始まり、全面核戦争に至る可能性は否定できない。日本の国益のために使いたいと思っても、米国がそう簡単に認めることはあり得ない。逆に米国が使うと決断した状況で日本が拒絶すれば、日米安保体制の崩壊につながりかねない。米国は日本の核武装を許さないし、日本は勝手に使おうと思っても使えない。
今日の日本について「核共有」を議論するのは飛躍しすぎている。その理由は次の通りである。
冷戦時代より陸上の脅威への対処を中心に考えてきた欧州に比べて、周辺が海である日本は、通常弾頭搭載巡航ミサイルや弾道ミサイルといった ⻑距離の攻撃能力について日米ともに能力の欠落があり、まずその強化を考えるべきである。攻めてくる相手国の軍艦や戦闘機を個別に撃つのか、どの程度の距離まで 近づいたら撃つのか、あるいは相手国の港湾施設や滑走路を破壊する⻑距離の攻撃能力がある通常兵器を保有して、そういう事態を未然に防 ぐのか。ちょうど国会で「敵基地攻撃能力」の議論がなされているが、国⺠的議論をきちんとすべきで ある。
核兵器は最終的に使用する決意がないと抑止力にならない。軍事的に核兵器を使用する決断を、日本国⺠が果たして支持するだろうか。プーチン氏がウ クライナを攻撃するのは、「米国はこのぐらいのことでは絶対核を使わない、軍事介入しない」と確信して いるからである。全面核戦争というのは、合理的な指導者が選べる選択肢ではない。ただ、どんな国 の指導者も追い詰められた状況で一線を 越えてしまうことはある。それが核兵器で起こると、本当に人類の未曽有の事態となる。たとえ核共有の核兵器であっても、本当に使うときは、日本の総理が命じて自衛隊が使うこととなる。そのことの歴史的意味を考えてもらいたい。日本の人的資源も経済的資源も、核共有とは違うところに使うべきである。
必要になれば米国の核の傘が機能し、日本が必要とした時に米国が助けてくれる信頼関係こそが、日米同盟の持つ抑止力である。そのためにも、軍事的なオペレーションについては今以上に緊密に、日米とその周辺のパートナー国であるオーストラリアや韓国などと協議しなければいけない。日本も米国に対して、NATOのような協議を要求し、必要ならばそのための制度を作ればいい。核共有をしなくても、核使用を含む戦略についての協議はできるし、やるべきである。究極の核戦争になる前の早い段階におけるさまざまな抑止力について、日本は議論を怠ってきたのではないか。そのような抑止力を掻いたままだと、究極的に核戦争に至るまでの抑止力を弱めることとなる。特に台湾海峡や朝鮮半島で有事があれば、邦人退避なども含めて幅広く想定しなくてはいけない。
実際には使えないものを持っていても、それで得られる万能感は幻想にすぎない。たとえお金や時間がかかっても、地道でしんどい努力を積み上げる必要がある。核共有は抑止力の近道ではなく、抑止力に近道はない。
筆者は政策研究大学院大学教授（国際政治）
第１に、核「共有」と言っても核兵器「保有」を意味するものではない。核兵器はacticalあくまで米国のもので、戦争で使う際に参加国が関与するので、運用全体に参加するという限りにおいて「シェア」と言われる。米国の核共有には、ドイ ツ、イタリア、ベルギー、オランダ、トルコの5N A T O加盟国が参加しており、ドイツでは、戦場単位の使用を想定した戦術核（B61という米軍の小型核兵器）を、ドイツ連邦軍の軍事基地の中で厳しい米軍の管理の下に保管しており、有事になれば、米軍がドイツ連邦軍に供与し、ドイツ連邦軍が自らの戦闘機（通常兵器と核兵器の双方を運用可能という意味で、「dual-capable aircraft（DCA）」と呼ばれる）に搭載して使用する約束となっている。この5カ国に計約100発のB61があると推定されている。
NATOは冷戦期、有事の際には通常兵器で優位に立つソ連側 地上軍の侵攻に対して戦術核兵器を投入する防衛戦略を基本としており、多くの核兵器が⻄ドイツ等に配備されていた。他方、フランスは「パリのために米国が核兵器を使ってくれるの か? ニューヨークを守るためには、米国はむしろパリを犠牲にするだろう」と考え、独自に核兵器を持つことを決めた。同様の疑念が欧州のNATO加盟国側で高まり、⻄ドイツ等が同調することを米国が恐れたため、米国の核兵器を一緒に運用する案が生まれた。核共有に参加する国が米国と2国間で取り決めを交わし、 1960年代末には全体のかたちがまとまった。
70年代のピーク時には欧州には7000発以上米国核兵器があり、それを削減してきたことを考えると、小型の核兵器が欧州に100発あることに果たして軍事的な意味はあるのだろうか？筆者はこれを実際の軍事的意味よりも米国の政治的コミットメントとして捉えている。 冷戦下の米ソにとって、第二次世界大戦の火種となり敗戦で東⻄に分裂したドイツが核を保有しないことが、安全保障上も地政学的にも重要だった。それを実現するために米国と同盟国、さらにはソ連が１０年間に渡り模索してたどり着いたぎりぎりの妥協が核共有であった。
第２に、核共有とは、米国の拡大抑止の同盟内の信頼性を維持し、かつ核拡散を防止するための制度である。NATOにはフランスを除く29加盟国が参加するNPG(核計画グループ)という協議の枠組みがあり、核共有されている核兵器はここで協議して承認されなければ使うことはできない。また、NPGでは、核の運用に限らず核政策全体についても参加国内で情報をシェアすることで核抑止力の信頼性を高めている。また、平時における核兵器の管理は厳格に米軍により行われるので、N P T（核拡散防止条約）体制にも密接に組み込まれている。
第３に、たとえ核共有をしても、その極めて重たい決断を参加国が勝手に下すことはあり得ない。どんなに小さくても核兵器を使うと、そこから核のエスカレーションが始まり、全面核戦争に至る可能性は否定できない。日本の国益のために使いたいと思っても、米国がそう簡単に認めることはあり得ない。逆に米国が使うと決断した状況で日本が拒絶すれば、日米安保体制の崩壊につながりかねない。米国は日本の核武装を許さないし、日本は勝手に使おうと思っても使えない。
今日の日本について「核共有」を議論するのは飛躍しすぎている。その理由は次の通りである。
冷戦時代より陸上の脅威への対処を中心に考えてきた欧州に比べて、周辺が海である日本は、通常弾頭搭載巡航ミサイルや弾道ミサイルといった ⻑距離の攻撃能力について日米ともに能力の欠落があり、まずその強化を考えるべきである。攻めてくる相手国の軍艦や戦闘機を個別に撃つのか、どの程度の距離まで 近づいたら撃つのか、あるいは相手国の港湾施設や滑走路を破壊する⻑距離の攻撃能力がある通常兵器を保有して、そういう事態を未然に防 ぐのか。ちょうど国会で「敵基地攻撃能力」の議論がなされているが、国⺠的議論をきちんとすべきで ある。
核兵器は最終的に使用する決意がないと抑止力にならない。軍事的に核兵器を使用する決断を、日本国⺠が果たして支持するだろうか。プーチン氏がウ クライナを攻撃するのは、「米国はこのぐらいのことでは絶対核を使わない、軍事介入しない」と確信して いるからである。全面核戦争というのは、合理的な指導者が選べる選択肢ではない。ただ、どんな国 の指導者も追い詰められた状況で一線を 越えてしまうことはある。それが核兵器で起こると、本当に人類の未曽有の事態となる。たとえ核共有の核兵器であっても、本当に使うときは、日本の総理が命じて自衛隊が使うこととなる。そのことの歴史的意味を考えてもらいたい。日本の人的資源も経済的資源も、核共有とは違うところに使うべきである。
必要になれば米国の核の傘が機能し、日本が必要とした時に米国が助けてくれる信頼関係こそが、日米同盟の持つ抑止力である。そのためにも、軍事的なオペレーションについては今以上に緊密に、日米とその周辺のパートナー国であるオーストラリアや韓国などと協議しなければいけない。日本も米国に対して、NATOのような協議を要求し、必要ならばそのための制度を作ればいい。核共有をしなくても、核使用を含む戦略についての協議はできるし、やるべきである。究極の核戦争になる前の早い段階におけるさまざまな抑止力について、日本は議論を怠ってきたのではないか。そのような抑止力を掻いたままだと、究極的に核戦争に至るまでの抑止力を弱めることとなる。特に台湾海峡や朝鮮半島で有事があれば、邦人退避なども含めて幅広く想定しなくてはいけない。
実際には使えないものを持っていても、それで得られる万能感は幻想にすぎない。たとえお金や時間がかかっても、地道でしんどい努力を積み上げる必要がある。核共有は抑止力の近道ではなく、抑止力に近道はない。
筆者は政策研究大学院大学教授（国際政治）
一般社団法人 日本英語交流連盟