Examined in this article are the battles that took place over the sea or in coastline areas, between the defending Goryeo forces and the invading Mongol troops, during the early 13th century. The issue became a rather sensitive topic recently, and a renewed perspective of that issue is required. Previously, “Jodo(槽島)” was believed to have been an island in the vicinity of the Seohae province(西海道), but at that time, Seohae-do was only upon the route that led to the Gaegyeong(開京) capital of Goryeo, and there is no indication that an assault upon the islands was launched from this location. Instead, right after the Jodo battle, in response to the Mongol troops ‘overall offensive targeting islands in the sea, the Goryeo government dispatched troops to the Jeolla-do(全羅道). Considering such move, and the whereabouts of the Mongol main battalion, it would be reasonable to assume that Jodo was located in a position near that province, which was certainly better equipped and prepared, in terms of supporting the government’s defense efforts that would have most definitely included ship building. The so-called “A-ju island(牙州海島)” battle was not a battle that took place upon the sea, as it was fought by Goryeo troops which returned (from the island) to the land. And considering other references in key records, which depicted the Mongol troops’ continuing offensive against the Chungju(忠州) area, it would be hard to describe the outcome of this battle as a victory for the Goryeo troops. The island in question seems to have been the Daebu-do(大府島), where a rather large military forces composed of Chungju soldiers was stationed. Han Chwi(韓就), the Sunmun-Sa(Provincial Magistrate in the region : 巡問使) of Chungju-do(忠州道), was not a military commander but a civilian official who received an order from the government to secure necessary number of troops for upcoming missions. Shortly after that, Goryeo troops tried to prevent Mongol forces from attacking Chungju, but failed, and as a result Chungju fell.