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An automatic marine seismic monitoring and recording instrument of recoverable design is discussed. The instrument is capable of measuring three components of earth motion and water pressure waves and is intended for use on the ocean bottom at depths to 10,000 feet. Most previous seismic data has been recorded at land-based stations and the collection of ocean-floor seismic information will materially add to the knowledge of origin and propagation phenomena. Data are recorded on magnetic tape in digital form. Seismic motion is recorded in the 1-10 cps band with a sensitivity below 0.1 millimicron of earth movement. Pressure information is recorded over the same bandwidth with comparable sensitivity. Up to eight hours of data can be recorded on a programmed cycle during each implanting of the instrument. Initial sea tests of the instrument indicate that the unit functioned as desired. Several events recorded during the test period appeared to give valid seismic information. One of these events is described. Simultaneous recording of pressure and velocity is expected to enhance detection capability. It is planned in a future program to collect additional seismic information in much deeper waters and at sites chosen for maximum quality data return. The data will represent the first extensive effort to collect and analyze three-component seismic (plus pressure) information at great ocean depths.