‘Gulf of Tonkin Incident is related to which one of the following?

China and Vietnam share the northern Gulf of Tonkin, where China has made new territorial claims. The Gulf, which has a crescent shape and is part of the South China Sea, shares borders with the Guangxi Zhuang Autonomous Region of China, the Leizhou Peninsula, Hainan Island, and the northwest coast of Vietnam. It connects to the South China Sea and Hainan Strait and is called the 'Beibu Gulf' in Chinese and 'Bac Bo Gulf' in Vietnamese. Notably, the 1964 Gulf of Tonkin Incident during the Vietnam War gave the Gulf of Tonkin historical significance.