A report in Japanese media claims that North Korea is building a nuclear-powered submarine in secret, and that the vessel will be completed and beginning sea trials within three years.

The report by Japan’s Sekai Nippo, citing an “informed” but unidentified “source familiar with the North Korean situation,” said the size of the nuclear-powered submarine under construction is unclear.

The Washington Times, which reported the development, said the paper could not independently verify the Japanese report, either through the Sekai Nippo or through U.S. intelligence sources. But the paper noted that, if true, it would significantly boost North Korea’s naval-based first-strike capability since no doubt the nuclear-powered sub would be outfitted with nuclear-tipped ICBMs.

North Korea currently operates a fleet of about 50-60 diesel-electric subs that are much louder and easier to detect than nuclear-powered boomers. [source]

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