The government on Wednesday again upgraded its estimated size of North Korea’s latest nuclear test to a yield of around 160 kilotons — more than 10 times the size of the Hiroshima bomb — as a leading member of the ruling Liberal Democratic Party said the country should debate the deploying of U.S. atomic weapons on Japanese soil.
Defense Minister Itsunori Onodera called Sunday’s nuclear test “vastly greater” than previous North Korean nuclear tests.
“(North Korea) is evolving not just their ballistic missiles but also their nuclear technology,” he added.
“We cannot rule out the possibility that this was a hydrogen bomb test,” Onodera said.
Onodera’s remarks came as LDP heavyweight and former Defense Minister Shigeru Ishiba weighed in on the controversial and emotional issue of Japan hosting U.S. atomic weapons later in the day, saying that the possibility should be discussed in light of the North’s growing nuclear threat.
Ishiba said doing so could help bolster the deterrent power of the Japan-U.S. alliance.
Japan relies on the U.S. “nuclear umbrella” for protection. In the wake of the atomic bombings of Hiroshima and Nagasaki during World War II, the country has upheld since 1967 its so-called three non-nuclear principles of not producing, possessing or allowing nuclear weapons on Japanese territory.
However, Ishiba, speaking on a television program, expressed his opposition to the idea of Japan possessing its own nuclear arsenal.
“If Japan — the only country to have suffered atomic bombings in war — arms itself with nuclear weapons, I think it means any other country should be allowed to have them,” he said.
Ishiba called the issue an “emotional” one, noting that it could spark public outcry but questioned whether any debate should be dismissed out of hand.
“Is it really right for us to say that we will seek the protection of U.S. nuclear weapons, but we don’t want them inside our country?” he asked.
“Not possessing, producing and bringing in nuclear weapons, and not even discussing (this matter) — is that really OK?” he added.
The Japanese government is stepping up efforts to beef up its defense capabilities amid North Korea’s nuclear and missile advances.
Pyongyang has labeled Sunday’s nuclear test a detonation of an advanced hydrogen bomb that can be mounted on an intercontinental ballistic missile. The test prompted an emergency meeting Monday of the United Nations Security Council in New York.
Japan’s latest estimate of that test’s yield far exceeded the 50-to-100 kilotons indicated by U.N. political affairs chief Jeffrey Feltman at the U.N. Security Council meeting.
Onodera said the new estimate was based on definitive seismic data from the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The group had informed Tokyo of its observation of a magnitude-6.1 quake during Sunday’s nuclear test, up from earlier provisional estimates of 5.8 and 6.0.
The government had initially put the yield at 70 kilotons, which is still far greater than the estimated yields of North Korea’s five previous nuclear tests. Tokyo had later raised the estimate to some 120 kilotons.
The atomic bomb dropped by the U.S. on Hiroshima on Aug. 6, 1945, had a yield of 16 kilotons and the one dropped on Nagasaki three days later had a yield of 21 kilotons. One kiloton has the explosive force of 1,000 tons of TNT.
While bombs like those dropped on Hiroshima and Nagasaki use atomic fission to release energy, hydrogen bombs use an initial fission reaction to force radioactive isotopes of hydrogen to fuse together, creating a far more destructive force.
Earlier Wednesday, Onodera held telephone talks with U.S. Defense Secretary James Mattis, with both agreeing to step up “visible pressure” on North Korea, the Defense Ministry said.
Speaking to reporters, Onodera said he told Mattis that Sunday’s test “was far greater (in scale) than previous nuclear tests and presents a new, more grave and pressing threat to our country’s security.” Mattis, he said, expressed the same view.
Onodera quoted Mattis as saying the United States will defend Japan, citing in particular the deterrence offered by the U.S. “nuclear umbrella.”
He also said Mattis had expressed his intention to actively cooperate on the Self-Defense Forces’ acquisition of the land-based Aegis Ashore missile-defense system.
In their roughly 20-minute conversation, the two defense chiefs also affirmed they will coordinate with South Korea on the North Korean crisis.
The pair had made similar commitments in their last phone call on Aug. 31, which followed North Korea’s launch of an intermediate-range missile over Hokkaido and into the Pacific Ocean.
After his call with Mattis, Onodera met Adm. Scott Swift, the commander of the U.S. Pacific Fleet, at the Defense Ministry to confirm their cooperation in responding to security issues.
Meanwhile, Senior defense officials from Japan, the United States and South Korea held a videoconference later in the day to discuss their response to North Korea.