HMNZS Tui, formerly USNS Charles H. Davis (T-AGOR-5), was one of nine Conrad class oceanographic ships built for the United States Navy (USN), that later saw service in the Royal New Zealand Navy (RNZN). Serving with the USN from 1963 to 1970, these ships were designed to perform acoustic experiments on sound transmission underwater, and for gravity, magnetism and deep-ocean floor studies.