Implications of N. Korean nuclear tests

The Yomiuri Shimbun

From left: Yu Koizumi, Shunji Hiraiwa and Yun Duk Min

The Yomiuri Shimbun North Korea announced it successfully tested a hydrogen bomb capable of delivery via intercontinental ballistic missile — the country’s sixth test of a nuclear device. Why did it conduct this test, which further escalates tensions between North Korea and the United States? How far have North Korea’s nuclear miniaturization efforts progressed and how should the international community respond? We asked Japanese and South Korean experts for their views.

(From The Yomiuri Shimbun, Sept. 4, 2017)


Will these weapons actually be deployed?

Yu Koizumi / Special researcher at Institute for Future Engineering

Compared to its previous nuclear tests, North Korea’s test on Sept. 3 was incredibly powerful. It was, perhaps, the first case of the country detonating a fusion-based hydrogen bomb rather than a fission-based atomic bomb. Thus, this must be considered as a successful nuclear weapon test that has fundamentally different principles, rather than a continuation of the same nuclear testing conducted until now.

However, it is not believed North Korea has been able to miniaturize the nuclear weapon at this initial testing stage to the extent that it could be fitted on an intercontinental ballistic missile. North Korean state media showed an image in which the chairman of the Workers’ Party of Korea, Kim Jong Un, inspects a gourd-shaped object purported to be a hydrogen bomb. Structurally, the object appears to adhere to the design of a hydrogen bomb. The large bulb is the atomic bomb used for initial detonation, while the small bulb is the structure in which the hydrogen bomb or warhead is placed. However, doubts remain as to whether the country could produce such a small hydrogen bomb so quickly.

Normally, one first experiments with a primitive hydrogen explosive device to demonstrate a nuclear fusion reaction can take place, and then moves on to developing such a small warhead. The point of that image may be to show that in the future, when the warhead is miniaturized to that point, it could be loaded on their new Hwasong-14 ICBM and used to attack the United States.

To what extent has North Korea miniaturized its nuclear weapons? I have paid close attention to the two nuclear tests that took place last year in January and September. In September, North Korea announced for the first time it had tested a nuclear warhead. Perhaps at this stage they aimed to have the ability to equip a missile with a low-strength weapon with anywhere from several to 10 kilotons of explosive strength.

In the case of the January test, while North Korea asserted it was a hydrogen bomb, the force of the blast was clearly too small to be a hydrogen bomb. Perhaps it was an atomic bomb test of the detonator used for a hydrogen bomb. In other words, it is possible that at last year’s stage, North Korea considered nuclear miniaturization a significant goal.

There are still challenges for North Korea to deploy a nuclear missile. First, if their new mid-range ballistic missiles, the Hwasong-12 and Hwasong-14 that were launched for the first time this year, are not test-launched several more times, they could not be said to be at the level of being weaponized. Neither missile has been launched at its maximum range, and North Korea has not been able to test the heat shield under the precise conditions that exist at the time of reentry into the atmosphere. As a result, the nation will likely conduct additional missile launches.

It is possible they also reached their goal for standard fission-based atomic bombs during the fifth test in September of last year. However, to complete a hydrogen bomb, they must test the miniaturized hydrogen warhead. As a result, one or two more tests are a possibility.

North Korea has moved to a new stage of its nuclear development. It has reached the point where the issue of North Korea’s nuclear development has become a global problem now that there is a possibility that North Korean weapons could reach the United States.

Although there is a low probability the United States will engage in military action in the immediate future, it cannot be discounted in the medium to long term. There is no doubt the problem of deciding how to prevent North Korea’s nuclear and missile development, or accepting it and looking for deterrents, has become quite serious.


Koizumi’s specialty is Russia’s military, security, and space policy. He assumed his current position in April 2011 after being a visiting researcher at the Institute of World Economy and International Relations at the Russian Academy of Sciences. His publications include, “Gunji Taikoku Russia” (Russia, a major military power). He is 35.

(This interview was conducted by Yomirui Shimbun Senior Writer Tatsuya Fukumoto.)


North Korea bets against U.S. military action

Shunji Hiraiwa / Professor at Nanzan University

North Korea aims to develop a missile equipped with a nuclear weapon capable of reaching the U.S. mainland. Though such a weapon would be valuable in bargaining with the United States, the international community currently believes the North has yet to attain such a capability. I believe that North Korea’s successive missile launches, including the Hwasong-14 intercontinental ballistic missile, and its nuclear tests, the most recent of which is thought to have been of a hydrogen bomb, are intended to demonstrate an ability to strike the U.S. mainland. These tests help reduce its “credibility gap.” With an increasingly powerful aresenal at its disposal, North Korea has become a greater threat.

Nevertheless, North Korea worries about possible U.S. military action and has attempted to suss out the United States’ red line since this spring. It began by test-firing an ICBM and continued its saber-rattling by threatening to land a missile near the U.S. territory of Guam. During these provocations, the North observed the United States’ reaction. On the U.S. side, President Donald Trump has hinted at a potential military response, though Defense Secretary Jim Mattis and others have repeatedly cautioned against such action. North Korea seems to have determined that the United States has a high threshold for military action, and that its conducting of nuclear tests will not elicit a retaliatory strike.

The economy is key to the Trump administration’s thought process. Military action could have devastating economic consequences, limiting the likelihood of such an outcome.

North Korea may next act on Sept. 9, its national foundation day. After considering the U.S. response to its nuclear test, it may fire a missile in the vicinity of Guam, as previously announced. It may also launch an ICBM that passes through Japanese airspace.

The United States currently relies on “starvation tactics” like economic sanctions, which take time to take effect. North Korea will continue its rapid succession of nuclear tests and missile launches before the sanctions begin to bite, rendering its adversaries powerless to act. It believes it can survive long enough to force the United States into negotiations.

Unfortunately, the international community will have difficulty in changing North Korea’s behavior through economic sanctions. While raising pressure on North Korea, Japan and the United States may have no choice but to consider negotiating with the rogue state. I believe a dialogue could emerge if the United States accepts China as a mediator. U.S. rhetoric has changed considerably, and it has lowered its threshold for initiating talks. Initially, the United States called for concrete steps toward North Korean denuclearization; now it simply demands a suspension of nuclear tests and missile test launches.

In addition to strengthening its defense cooperation with the United States, Japan should reach out to China and Russia. If the United States decides to negotiate with North Korea, circumstances could rapidly evolve. While increasing pressure on North Korea, Japan, the United States and South Korea should maintain close links. This would help Japan harmonize its response with the United States should the latter launch negotiations.


Hiraiwa specializes in North and South Korean political diplomacy. He assumed his current position after serving as special investigator at the Japanese Embassy in China and as professor at Kwansei Gakuin University, among other roles. His publications includes, “Kitachosen wa Nani wo Kangaete Iru Noka” (What is North Korea thinking?) (NHK Publishing). He is 57.

(This interview was conducted by Yomiuri Shimbun Staff Writer Keita Ikeda.)


Take a closer look at the U.S. nuclear umbrella

Yun Duk Min / Professor at Hankuk University of Foreign Studies

North Korea has been steadily developing nuclear weapons, just as it planned. Using the U.S.-South Korea joint military exercises and resistance to the administration of U.S. President Donald Trump as a pretext, it has decided that conducting a nuclear test is necessary according to its own schedule, and it has achieved it.

Compared to previous nuclear tests, the latest test demonstrated a significant increase in explosive power. It may be safe to think that North Korea’s claim to have succeeded in developing a hydrogen bomb is true. In response to doubts in some sectors of the United States and South Korea that North Korea has been able to miniaturize a nuclear bomb to be loaded onto a ballistic missile, this test may have demonstrated that the task has been completed.

For North Korea, the one remaining challenge, in terms of nuclear and missile development, is the reliability of submarine-launched ballistic missiles. It is likely that the country will soon test its new type of SLBM, known as the Pukguksong-3. There is also the possibility that a new type of ICBM never tested before, the Hwasong-13, could be launched over the Japanese archipelago.

It is extremely dangerous for Kim Jong Un, chairman of the Workers’ Party of Korea, to play with fire by considering ICMBs as the ultimate deterrent. The U.S. administration seems to have already decided that it can undertake military action in line with international law, in the event that North Korea makes an “enveloping fire” off the coast of the U.S. territory of Guam using ballistic missiles. However, it will be difficult to protect Seoul, and when you consider that there are approximately 200,000 American people in South Korea, military actions such as preemptive strikes against North Korean missile facilities and other targets would prove extremely difficult.

If Kim Jong Un is wise, he will enter into a peace treaty with the United States in order to achieve a tacit nod toward his country’s nuclear armament in return for abandoning ICBM development. There is the possibility that U.S. President Donald Trump would respond to this under the pretext of gradual denuclearization.

In this case, only the development of ICBMs would cease, while the development of nuclear weapons would remain. The countries in the worst position would be Japan and South Korea. Such a situation might affect the reliability of alliances.

China’s position is complicated. It appears they are beginning to think that as long as North Korea does not directly provoke China, its ICBM development can be accepted. Within the United States, negotiations linking North Korea’s nuclear abandonment with the withdrawal of U.S. forces from South Korea have been proposed by people such as former U.S. Secretary of State Henry Kissinger.

If China thinks that North Korea’s possession of ICBMs would lead to a withdrawal of U.S. troops from South Korea, it may not cooperate with strong sanctions.

What is important for Japan and South Korea is to fully secure the deterrent power of U.S. nuclear weapons. Using nuclear weapons to deter nuclear weapons is common sense. One idea is to deploy cruise missiles with nuclear warheads on U.S. nuclear submarines that are deployed in areas around the Korean Peninsula.

It is necessary for Japan, the United States and South Korea to closely discuss the issue of the provision of the nuclear umbrella.


Yun specializes in North Korean nuclear issues, among others. He received his doctorate from Keio University. He was chancellor of the Korea National Diplomatic Academy from 2013 to May 2017. He is 57.

(This interview was conducted by Yomiuri Shimbun Correspondent Kentaro Nakajima.)


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