In 645, Emperor Taizong of Tang(唐太宗) lost the war with Goguryeo. Two years later, Taizong prepared for invasion again. It was concluded that intermittent attacks were continued with the water force, exhausting Goguryeo, and making all-out attacks. Between 647 and 648, the army invaded Goguryeo and fought many battles, showing off its dominant power. The random landing attack put Goguryeo in trouble. The efficiency of defense declined because the party’s leadership did not know where it would attack. Goguryeo’s expected defense area expanded and was forced to consume.
On the contrary, the landing war trained Chinese water forces and accumulated local information about Goguryeo. Judging that Goguryeo was devastated, Taizong tried to invade with 300,000 people. Since July 648, ships with a length of 300m and a width of 150m have been built in Tsuan, and 1,450 ships have been built at the shipyard of the Yangtze River. The innate factor that made it possible was in China. China had a huge hinterland that was suitable for ports and easy to explore the ocean. In the Yangtze River area, there were many people engaged in water business, and they had a habit of pursuing wealth through waterways. There was a vast water industry base.
However, with the death of Taizong in 649, the naval enhancement was suspended, but it was inherited to his son. Emperor Gojong of Tang(唐高宗) inherited naval forces trained by his father, maritime military bases built in various places, and skilled shipbuilders and shipyards.
In 660, Gojong sent 1,800 fleets carrying 130,000 naval forces to destroy Baekje in 10 days. Furthermore, in 661, the fleet of the Tang Dynasty landed on the Daedong River and surrounded the Goguryeo capital. And in 663, the Tang Dynasty naval forces defeated the Japanese fleet on the Baekchon River in Baekje.
However, the existence of Goguryeo naval forces against Tang Dynasty naval forces is invisible. Goguryeo did not reinforce the naval forces, but focused on enhancing the army. The sea is limited in that it can be used for defense, and ships with a lifespan of about 7 years are more consumable than forts. In order to maintain a certain number, continuous shipbuilding is required and enormous finances are required. Goguryeo cannot compete with the Tang Dynasty for fleet construction.
The Tang Dynasty occupied the sea, and uncertainties in the sea increased. It hit Goguryeo’s logistics economy hard and increased social costs. The Tang Dynasty, which has a powerful naval force, has become much easier to invade Goguryeo. The loss of the sea would have been one of the environments of Goguryeo’s destruction.