| Pic: | Gulf of Tonkin location.gif |
| S: | 北部湾 东京湾 |
| T: | 北部灣 東京灣 |
| P: | Běibù Wān Dōngjīng Wān |
| J: | Bak1 bou6 waan1 Dung1 ging1 waan1 |
| Hain: | Pak-pōe oân Tang-kiann oân |
| L: | Northern Gulf Gulf of Tonkin |
| Qn: | Vịnh Bắc Bộ Vịnh Bắc Phần Vịnh Đông Kinh Vịnh Bắc Việt |
| Chuhan: | 泳北部 泳北份 泳東京 泳北越 |
The Gulf of Tonkin is a gulf at the northwestern portion of the South China Sea, located off the coasts of Tonkin (northern Vietnam) and South China. It has a total surface area of . It is defined in the west and northwest by the northern coastline of Vietnam down to the Hòn La Island, in the north by China's Guangxi Zhuang Autonomous Region, and to the east by the Leizhou Peninsula and Hainan Island.
The name Tonkin, written "Vietnamese: 東京" in chữ Hán characters and Vietnamese: Đông Kinh in the Vietnamese alphabet, means "eastern capital", and is the former toponym for Hanoi, the present capital of Vietnam. It is not to be confused with Tokyo, which is also written "Japanese: 東京" and also means "eastern capital". During the French colonial era, the northern region of today’s Vietnam was called Tonkin.
Bắc Bộ is the native Vietnamese name of Tonkin. The bay's Vietnamese and Chinese names – Vietnamese: Vịnh Bắc Bộ and Chinese: Běibù Wān, respectively – both mean "Northern Bay".
The Gulf of Tonkin is a relatively shallow portion of the Pacific Ocean; the majority of the gulf's ocean floor is less than 75m (246feet) in depth, and no part of the gulf is submerged in more than 100m (300feet) of water.[1]
See main article: Gulf of Tonkin incident. On 4 August 1964, United States President Lyndon B. Johnson claimed that North Vietnamese forces had twice attacked American destroyers in the Gulf of Tonkin.[2] Known today as the Gulf of Tonkin Incident, this event spawned the Gulf of Tonkin Resolution of 7 August 1964, ultimately leading to open war between North Vietnam and South Vietnam. It furthermore foreshadowed the major escalation of the Vietnam War in South Vietnam, which began with the landing of US regular combat troops at Da Nang in 1965.