North Korea Claims It Launched Two Submarine Launched Cruise Missiles
What is significant about cruise missiles launched from submarines is that missile defenses in the ROK now have to be positioned to account for them. Missile defense planning is much easier when you know the general direction of where threat targets are coming from. In the case of North Korea they fly in from the north and across the DMZ towards high value targets in South Korea. The ROK and the U.S. position air defense assets as required against these threat trajectories.
However, if missiles can be fired at the ROK from the east and the west via naval assets, then air defense positioning has to be adjusted or increased to compensate. With that all said, I doubt any North Korean naval asset would survive very long in a conventional war with the U.S. and the ROK, regardless these threats still need to be planned for:

North Korea said Thursday it tested two types of submarine-launched strategic cruise missiles in the East Sea the previous day.
“The test-fire aimed to examine the current mobilized posture of the underwater combat systems and contributed to getting the Navy skilled in performing its strategic missions and showcasing high reliability, trustworthiness and ability of the war deterrents of the DPRK,” the North’s Korean Central News Agency said in an English dispatch.
You can read more at the link.

