In cooperation with the U.S. military, the Defense Ministry in Tokyo is analyzing how much of a threat North Korean submarine-launched ballistic missiles may pose.

North Korea claims to have succeeded in test-firing a new-type of SLBM, the Pukguksong-3, apparently in reference to a projectile launched by the country on Wednesday that fell into Japan’s exclusive economic zone.

SLBMs will present a significant threat if deployed. But the ministry believes it will take time before the sophisticated missiles are loaded into a submarine that can be used in war operations.

According to the ministry and other sources, North Korea owns outdated diesel submarines acquired from China and the former Soviet Union.

When North Korea fired SLBMs in 2016, the country is believed to have used a renovated 1,500-ton submarine obtained from the former Soviet Union.

Pyongyang is reportedly building a larger submarine capable of launching SLBMs. But a senior ministry official said, “We have no information that any new submarine has been launched.”

The latest SLBM may have been fired from a launcher placed under the surface of the sea.

Pukguksong SLBMs are about 10 meters tall. SLBMs need to stand erect when loaded into a submarine.

The United States has the Ohio-class ballistic missile-capable nuclear submarines, which are 170 meters long and have a displacement of 19,000 tons.

Their length is about double that of Maritime Self-Defense Force submarines, and their displacement more than six times.

“A submarine requires sophisticated construction techniques, including those to weld together steel materials that can withstand strong water pressure,” a senior SDF official said.

“A big vessel needs a lot of power. Operations require deep knowledge of undersea terrain,” the official continued.

“I guess North Korea, which has outdated submarines, needs a substantial amount of time to start operations” of a ballistic missile-capable submarine, according to the official.

If such a submarine is deployed, North Korea would be able to carry out a surprise attack on Japan from waters near the country using short-range missiles.

Even worse, North Korea would be able to maintain the capability to hit back even if it receives a first strike.

“If such a submarine is deployed, Japan and the United States will conduct intensive surveillance using their submarines and patrol aircraft,” a Japanese government source said.

It would be relatively easy to see whether such a submarine has left port through satellite-based surveillance, informed sources say.

Under the Sea of Japan, sounds of a submarine are relatively easy to hear in many areas because of the water depths and temperatures, according to the sources.

But it would be difficult to detect such sounds if submarines stay inside North Korean territorial waters, the sources said.

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