North Danger Reef

North Danger Reef (Vietnamese: Cụm Song Tử) is one of the seven major reefs / banks / etc. in the Spratly Islands area of the South China Sea. It is the most North Western of the features of the Spratly Islands, located to the NW of Dangerous Ground.

The reef is a large (8.5 nautical miles) approximately circular atoll with a central lagoon (~20m deep). The surrounding reef is shallow.

Fishermen from Champa were likely the first people to discover the reef. However, later on, the Vietnamese would show interest for the reef.

From the 15th century onward, Vietnamese kings began to pay attention to the islands in the South China sea.

In 1776, Le Quy Don wrote at Phu Bien Tap Luc about these islands, as well as the establishment and operation of the Paracel fleet (Vietnamese: Hải Đội Hoàng Sa) and the Northern fleet (Vietnamese: Hải Đội Bắc Hải) of Vietnam.

In 1838, Emperor Minh Mang of Nguyễn dynasty Vietnam ordered the measurement and illustration of a map for the area. It was called the "Dai Nam Nhat Thong Toan Do", in which it claimed the Spratly and Paracel Islands for Vietnam during Nguyễn dynasty era.

When Vietnam was a French colony under French Indochina, the French Government continued to manage North Danger Reef along with the Paracel and Spratly Islands.

In 1935, China announced its claims and named the North Danger Reef. It is called: "Gemini" (Chinese: 双子群礁).