In the dock along the Huangpu River waterfront in Shanghai, a steel leviathan lies quietly at anchor. Its silvery-gray hull is as sharp as a blade, and its 76-meter length casts a deep shadow on the riverbank. This is the submarine "Great Wall 191" — China's first generation of domestically designed and built conventional-powered submarine, and the "underwater dragon" guarded by countless naval officers and soldiers with their youth. Remember to follow me; in the next episode, we will go inside the submarine.