https://en.wikipedia.org/wiki/Battle_of_the_Paracel_Islands
During the battle, the South Vietnamese fleet detected two more Chinese warships rushing to the area. China later acknowledged these were the
Hainan-class submarine chasers 281 and
282. Despite South Vietnamese reports that at least one of their ships had been struck by a missile, the Chinese insisted what the South Vietnamese saw were
rocket-propelled grenades fired by the crew of #389 and that no missile-capable ships were present, and the Chinese ships closed in because they had no missiles. The South Vietnamese fleet also received warnings that
U.S. Navy radar had detected additional Chinese
guided missile frigates and aircraft on their way from Hainan.
South Vietnam requested assistance from the U.S.
Seventh Fleet, but the request was denied.