13 screws, one HASL man operated the winch and another the winch brake, the boatswain handled the lines to the cable from the boom and brought the probe aboard with the help of a seaman. The meter block had to be removed from the davit and the hydrographic cable installed for Nansen sampling and plankton tows. The removal and replacement of the probe required about 45 min. From the winch drum, the cable went through a meter wheel block on the davit, and was held clear of the port screw by a boom near the stern. About 150-200 m of cable were required to give an estimated probe depth of 5-10 ft when cruising at 17 knots. During bathythermograph measurements, the probe sank somewhat (speed 3-4 knots) and gave a lower reading on the chart. Most of the problems encountered would not arise in continuous monitoring at slower speeds. Conclusions 1. Sea water and plankton samples show the existence of widespread low-level activity in the Pacific Ocean. Water activity ranged from 0-570 d/min/liter and - plankton from 3-140 d/min/g wet weight. 2. There is some concentration of the activity in the main current streams, such as the North Equatorial Current. The highest activity was off the coast of Luzon, averaging 190 d/min/liter down to 600 m (April 1, 1955). 3. Analyses of fish indicate no activity approaching the maximum permissible level for foods. The highest activity in tuna fish was 3.5 d/min/g ash, less than 1 percent of the permissible level, 4. Measurements of plankton activity offer a sensitive indication of activity in the ocean. 5. Similar operations would be valuable in assessing the activity from future tests. and in gathering valuable data for oceanographic studies.