 By August 1966, Nygren was a captain, but that month he voluntarily accepted a reduction in rank to commander so that he could go back to sea.That month, he reported aboard the ocean survey ship USC&GS "Surveyor" (OSS 32) as her executive officer.She operated in the North Pacific Ocean, conducted experiments in the Line Islands, carried out a project around islands off Mexico with Mexican scientists embarked, and worked in the Bering Sea, along the southeast coast of Alaska, and in the Aleutian Islands.