The study of surface waves in the deep ocean can be carried out effectively by using a new technique: measurement of accelerations of a small water mass well below the surface. Instrumentation for carrying out such measurements is described in detail, including a special accelerometer, neutrally buoyant case, long lightweight slack wire, and data-recording equipment. Some initial results achieved with this equipment are shown and the possibility of broader applications of this technique for wave and gravity measurements at sea are discussed briefly.