A U.S. think tank has observed a surge in submarine-related activities at North Korea’s Sinpo shipyard, saying that the North may carry out submarine-launched ballistic missile(SLBM) tests this summer. 

Citing satellite imagery, the Beyond Parallel website run by the Center for Strategic and International Studies(CSIS) said on Thursday that during the past five weeks, there has been an exceptional surge of activity at Sinpo. 

Beyond Parallel said the North has “undertaken moves” of the Hero Kim Kun Ok ballistic missile submarine(SSB), the 8.24 Yongung experiment ballistic missile submarine(SSBA), and the submersible missile test stand barge.

The website said that these three vessels represent core elements of North Korea’s ballistic missile submarine, SLBM, and submarine-launched cruise missile(SLCM) development programs.

It added that this overall level of activity may be a sign of the commencement later this summer of sea trials for the Hero Kim Kun Ok, preparations for the resumption of SLBM and SLCM flight testing, or both.

The website said that the level of activity and success these vessels achieve will heavily influence future North Korean development of submarine technology, designs and operational procedures.