Bach Long Vi Island - China surrendered all claims in return for Viet recognition of Paracels and Spratleys as belonging to China.
In 1887, a convention between China (Qing Dynasty) and France made Qing government ceded the island to French Indochina (Annam Protectorate).[5] However, this was not an acceptable result for China. In the contemporary published map of People's Republic of China and other nations, this island still remained a part of China(Goode's World Atlas, Rand McNally, 1933). Besides, some foreign scholars regarded this island had been China's territory at least to 1950.[6]
During the World War II, Japanese army forced the French out of Indochina and seized the island.
In 1949, the Chinese Communist won the Chinese Civil War against the Chiang Kai-shek's army.
In 1955 the People's Republic of China drove the Chiang Kai-shek's army away and seized the island.[4]
On January 16, 1957, China's government transferred the island to North Vietnam's government.[4] On that day, the Prime Minister of Vietnam signed Decree number 49/Ttg which stipulated that Bạch Long Vĩ island is a “Xã” (village) and belongs to Haiphong City.
https://en.wikipedia.org/wiki/B%E1%BA%A1ch_Long_V%C4%A9_island
