During the 1960s, hydrophone arrays at seven MILS stations around the north Pacific were used to locate earthquakes using the T phase. Much of our knowledge of the characteristics of the T phase and of oceanic earthquakes came from this early study, which located more than 20 000 events in slightly more than 2 years. There were 3794 sources located by the T-phase project in 1966 in the Aleutian Islands region compared to 431 earthquakes located by the coast and geodetic survey in the region. Earthquakes of about 0.7 magnitude units lower than the C&GS threshold could be located by T phase. Study of these events resulted in recognition of mechanisms for propagation of T-phase energy from the earth to the ocean. Classical slope generation at continental margins and islands feeds energy directly into the sound channel by multiple down-slope reflections. Scattering from the ocean floor and surface appear to account for the energy in the T phases from earthquakes beneath the deep ocean floor. More recent long-term recording of the Wake Island hydrophones has resulted in characterization of variations in ambient noise and of the earthquake P[inf o] and S[inf o] arrivals, which appear to be trapped in the oceanic lithosphere.