Sea Trials. Sea trials were carried out at Aarhus, Appenrade, and Frederizia in Den-mark, in depths of 10 to 13 fathmos. No systematic attempt was made to measure the sound output from ships by means of hydrophones. The output voltage from the mine re-ceivers was measured, however, for a number of targets, including the trials ship Greif freighters up to 5.000 tons, a tug, and small motor boats. The voltage output was from 1 to 1,000 microvolts from the ships, and the sea noise was less than one microvolt.