In fact during this period, when Hanoi was relying heavily on the Chinese for support, the Hanoi authorities seem to have recognized the Spratlys and the Paracels as Chinese territories. Three bits of evidence for this are often cited by China.33 The first is a statement by Vietnamese Deputy Foreign Minister Ung Van Khien to Chinese Deputy Foreign Minister Li Zhimin in which the former indicated that Vietnam had recognized the Paracels and the Spratlys as Chinese territory since the days of the Song dynasty. The second is Pham Van Dong's letter dated September 14, 1958. It supported China's statement, extending its territorial waters twelve nautical miles. The statement clearly mentioned the Paracels and Spratlys by name as belonging to China. Third, in May 1965, the (North) Vietnamese Foreign Ministry criticized the United States for defining "part of China's Paracels" as a "fighting operation area."34
When victory was finally attained over the South, however, Hanoi was anxious to pick up all the pieces and claims left by the fallen regime. It acknowledged later that it had indeed previously acquiesced in China's claims to the islands but argued that times since then had changed.
At that time, Vietnam had to struggle against American intervention and aggression. . . . During this period, China regarded American imperialism as its main enemy and firmly supported the anti-American war of the Vietnamese people and was the "Vietnamese people's great rear base." China was one of the biggest aid donors to Vietnam. In the anti-American struggle, China and Vietnam became real friends. Relations between the two were "as close as lips and teeth." . . . During this period of opposing a much stronger enemy, the more Vietnam could let China fight hand in hand with Vietnam, the more advantageous for Vietnam to prevent America from using these two archipelagoes, and avoid attacks from the South China Sea [the East Sea in Vietnamese]. We have to understand the above statements in this spirit.36
With this rationale, in 1975 Vietnam asserted its claims to both the Paracels and the Spratlys and physically took possession of the six Spratly islands that the former South Vietnamese regime had occupied. In later years other islands were added.