In early September, Li Hongzhang decided to reinforce the Chinese forces at Pyongyang by employing the Beiyang fleet to escort transports to the mouth of the Taedong River. About 4,500 additional troops stationed in the Zhili were to be redeployed. On September 12, half of the troops embarked at Dagu on five specially chartered transports and headed to Dalian where two days later on September 14, they were joined by another 2,000 soldiers.
Initially, Admiral Ding wanted to send the transports under a light escort with only a few ships, while the main force of the Beiyang Fleet would locate and operate directly against Combined Fleet in order to prevent the Japanese from intercepting the convoy. But the appearance of the Japanese cruisers Yoshino and Naniwa on a reconnaissance sortie near Weihaiwei thwarted these plans. The Chinese had mistaken them for the main Japanese fleet. Consequently, on September 12, the entire Beiyang Fleet departed Dalian heading for Weihaiwei, arriving near the Shandong Peninsula the next day.
On 15 September, the Imperial Japanese Army converged on the city of Pyongyang from several directions. The Japanese assaulted the city and eventually defeated the Chinese by an attack from the rear; the defenders surrendered. Taking advantage of heavy rainfall overnight, the remaining Chinese troops escaped Pyongyang and headed northeast toward the coastal city of Uiju. Casualties were 2,000 killed and around 4,000 wounded for the Chinese, while the Japanese casualties totaled 102 men killed, 433 wounded, and 33 missing. In the early morning of 16 September, the entire Japanese army entered Pyongyang.
The Chinese warships spent the entire day cruising the area, waiting for the Japanese. However, since there was no sighting of the Japanese fleet, Admiral Ding decided to return to Dalian, reaching the port in the morning of September 15.
Admiral Ding correctly assumed that the next Chinese line of defence would be established on the Yalu River, decided to redeploy the embarked soldiers there. On September 16, the convoy of five transport ships departed from the Dalian Bay under escort from the vessels of the Beiyang Fleet which included the two ironclad battleships, Dingyuan and Zhenyuan. Reaching the mouth of the Yalu River, the transports, disembarked the troops were and the landing operation lasted until the following morning.
On September 17, 1894, the Japanese Combined Fleet encountered the Chinese Beiyang Fleet off the mouth of the Yalu River. The naval battle, which lasted from late morning to dusk, resulted in a Japanese victory. Although the Chinese were able to land 4,500 troops near the Yalu River by sunset the Beiyang fleet was near the point of total collapse, most of the fleet had fled or had been sunk and the two largest ships Dingyuan and Zhenyuan were nearly out of ammunition. The Imperial Japanese Navy destroyed eight of the ten Chinese warships, assuring Japan's command of the Yellow Sea. The principal factors in the Japanese victory was the superiority in speed and firepower. The victory shattered the morale of the Chinese naval forces. The Battle of the Yalu River was the largest naval engagement of the war and was a major propaganda victory for Japan.