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Natural and man-made seismic activity in ocean environments can be recorded in situ by self-contained ocean-bottom seismograph stations. Development of such operational capability was accomplished during 5 yr of testing and evaluation of three generations of ocean bottom systems. The first and second generation systems were attached by cable to a surface buoy and had less than 12-h recording capability. The present system is allowed to free-fall to operational depths of 4100 fathoms without the requirement of cable or attachment to the surface. The unit records three components of seismic activity and water pressure in the band 1–10 Hz on a 30-day tape recorder. Signals are amplified by low-frequency parametric amplifiers. A digital clock with a timing accuracy of 0.5 sec within a 30-day period is used for timing of data. Release of the system is accomplished by burning a fuse wire. Upon release, the sphere rises to the surface, where a beacon light and radio transmitter are activated to assist recovery operations. With existing technology other parameters can be measured; such as, salinity, temperature, ambient light, sound velocity, depth, gravity, magnetics, and water currents.