Updated following discovery of better detective work. Check out Joseph Dempsey's analysis on Twitter
Recent TV footage from North Korea’s suggests that the country’s sole Sinpo Class (aka Gonae Class) ballistic missile submarine (SSB) has relocated from the quayside at the factory where it was built, to an isolated peer at a submarine base. Analysis suggests that the new base is the major submarine base at Cha'aho (not on the island of Mayang-do as this post originally proposed).
These images are harder to locate. Note that the boat is moored on the opposite side to the above images.
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The Sinpo Class is North Korea’s first ballistic missile submarine and the largest submarine ever built in the country. It is however very small for a ballistic missile boat and can only carry a single missile tube which is located below the sail. The NK-11 “북극성-1” (Pukgeukseong-1 = 'North Star-1' = 'Polaris-1') missile is a clone of the Soviet era R-27 missile and is consequently likely to be much shorter ranged than submarine launched ballistic missiles used by most other nuclear powers.
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North Korean SSBN program - Sinpo Class