ll monitoring water was constructed by the HASL, NYOO. This in- stallation differed from that used during Operation Troll” in that the probe was mounted in a cylindrical, rubber-lined tank, 4 feet in diameter and 6 feet long (Fig. 1). Water from the sur- face of the sea was passed through the tank at the rate of about 30 gallons per minute. The sensing probe contained a plastic phosphor three inches in diameter and thirty inches long, a photomultiplier tube, and a battery-operated preamplifier. The probe unit was connected to a control box inside the ship by two coaxial lines, the high voltage line and the signal line. The control box contained an AC-operated high voltage supply and a beamplifier with output scales of 5, 50, 500, and 5,000 microroentgens. The signal from the control box was fed into an Esterline Angus recorder which The was operated at a chart speed of three inches per hour. scintillation unit was operated throughout the duration of the trip. METHODS OF ANALYSES Preliminary analyses of the plankton and surface water were carried out on board the WALTON. Further determinations were made at the EMBL and at the Applied Fisheries Laboratory. Counting Equipment: Samples were prepared on 14-inch Stainless steel plates and counted with a 2 inch Anton tube in _. ¥ Harley, John H., Editor, Operation Troll, NYO-4656, March 1956, rs tnd a atc e ay FTE