The Battle of the Yalu River (; Japanese:), was the largest naval engagement of the First Sino-Japanese War, and took place on September 17, 1894, the day after the Japanese victory at the land Battle of Pyongyang. It involved ships from the Imperial Japanese Navy and the Chinese Beiyang Fleet. The battle is also known by a variety of names: Battle of Haiyang Island, Battle of Dadonggou, Battle of the Yellow Sea and Battle of Yalu, after the geographic location of the battle, which was in the Yellow Sea off of the mouth of the Yalu River and not in the river itself. There is also no agreement among contemporary sources on the exact numbers and compositions of each fleet.