http://en.wikipedia.org/wiki/Battle_of_Hoang_Sa

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The battle
In the early morning of January 19, 1974, Vietnamese troops from HQ-5 landed on Duncan Island (Quang Hòa in Vietnamese) and came under fire from Chinese troops. Three Vietnamese soldiers were killed and two others were injured. Outnumbered, the Vietnamese ground forces withdrew by landing craft, but their small fleet itself did not: instead, they drew up close to the Chinese ships in a tense standoff.

At 10:24 a.m., all four Vietnamese ships opened fire. The ensuing sea battle lasted for about 40 minutes, with numerous vessels on both sides sustaining damage. The Vietnamese, trained and equipped only for coastal and river combat, were outgunned and despite a spirited effort were forced to disengage. The Nhật Tảo (HQ-10) could not retreat because her last working engine was disabled in the battle: the ship's crew was ordered to evacuate, but her captain, Major Ngụy Văn Thà, remained under fire and went down with his ship. The rest of the force retreated northward and westward to the vicinity of Pattle, Robert, and Money Islands.

The next day, Chinese jet fighters and ground-attack aircraft from Hainan bombed the three islands, and were followed up with an amphibious landing force. The South Vietnamese Marine garrison was captured, and the naval force retreated to Đà Nẵng.

While the battle was going on, the Vietnamese fleet detected two Chinese reinforcing warships rushing to the area; China later acknowledged that these were the Hainan-Class submarine chasers #281 and #282. Despite reports that at least one Vietnamese craft had been struck by a missile, China insisted that no missile-bearing ships were involved in the battle. In addition, the South Vietnamese fleet also received warnings from the United States that their naval radar had detected additional Chinese guided missile frigates and MIG jet fighters on their way from nearby Hainan. South Vietnam requested assistance from the US Seventh Fleet, but the request was rejected.