Abstract Operation Trollwas a joint undertaking of the AEC and ONRto evaluate residual radioactivity inthe Pacific Ocean a year after the Pacific nuclear tests held in the spring of 1954. The cutter ROGER B. TANEY was assigned to the operation by the US Coast Guard, and measurements were made over a course of 17,419 miles lasting from February 25 to May 3, 1955, Widespread low-level activity was found in sea water, plankton and fish samples, but none of the levels was high enough to cause concern as a possible hazard. The results do have scientific value, however, and are presented in full asan aid to other studies. ill