Decimating NK naval base in the area is one of the plan, I heard. As far as I know, the whole place has been thoroughly mapped, including underground caves to house submarines and shore artillery bunkers.
If a naval base is destroyed it is visible for the journalists, it is perhaps better to take out submerged subs first. Then no one knows if a Nork vessel is missing or not. But it sends a strong message to them when the subs get silent.
The peninsula on the DPRK side down into the West Sea from whence these attacks on South Korea were launched, and also the little island just south of there, these face Yongpyongdo, and could be attacked by South Korea, in fact, should be attacked and decimated, or at least put of out notice. Window: 48 hours max.