When the 1953 Armistice was concluded between the U.N. and North Korea, agreement over a maritime extension of the demilitarized zone was not achieved. In 1955, DPRK proclaimed territorial waters extending . from the coastline. Other than this, North Korea did not explicitly dispute or actively violate the NLL until 1973. First, the North Korean negotiators at the 346th meeting of the Military Armistice Commission challenged the status of the line. North Korea followed this up by sending large groups of patrol ships over the NLL on about 43 occasions in October and November. North Korea states that it had not been informed of the existence of the line, which is now confirmed by declassified U.S. diplomatic cables, so it could not dispute it earlier.