That same year France launched a punitive expedition against Korea, invading and occupying portions of Ganghwa Island in the fall of 1866. At the first battle, the Korean infantry division lost heavily, and General Yang Heon-su concluded that only a large cavalry division could stand up to French firepower. An ambush by Korean forces on a French party attempting to occupy the strategically located Cheondeung Temple 傳燈寺 on the island's south coast resulted in French casualties. French realization that they were far outnumbered and outgunned forced them to abandon the island and their expedition. The entire incident later became known as the byeong-in yang-yo, or foreign disturbance of the byeong-in year (1866).