The Northern Limit Line is interesting in that neither ROK nor UN forces seized the islands that define the line. They were seized by bands of North Korean anti-Communist guerrillas known as ‘Donkeys’ to the Americans. These “Dong-il” (Reunification) bands were largely composed of pre-war inhabitants of Hwanghae (Yellow Sea) Province who had fought a delaying action against the Communists in the hard winter of 1951, and withdrawn to the islands, where they refused to join the ROK forces and maintained a two year maritime guerrilla campaign in hopes that their homeland would be retaken by the UNC. To free up guerrilla manpower for operations within Hwanghae Province, the islands were garrisoned by units of the ROK Marine Corps, who remain there to this day.
So the ROK has as much right to hold those islands as the North Koreans do to occupy land below the 38th Parallel. North Korean holdings include present day Haeju, which lies just three kilometers beyond PyeongYeong island (referred to as PY-Do), which is within the NLL and where the Spirit Tablets of the North Korean anti-communist guerrilla bands are located.
Never heard that before, so I took a look around, and found a good piece on the Donkey Unit in the Seoul Shinmun (along with the photo above). Sadly, since they didn’t joint the ROK Army and took their orders directly from the Americans, they’ve become something of a “forgotten unit” in a “forgotten war.”
Also very worth reading is Andy Salmon’s piece for the BBC on the history of the NLL.