INTRODUCTION From 12-20 December, 1966, Robert DeLong and Patrick Gould conducted pelagic observations off the coast of Southern California. They were guests of the U.S.S. Henderson (D.D. 785), and were present on a "not to interfere" basis. Watches were maintained from sunrise through sunset for the entire trip. Periodic nocturnal checks were made, but the poor weather conditions, principally fog, and the fact that the ship was running under blackout conditions, prohibited any extensive nocturnal watches. Weather and locality data were provided by the ship's navigator. The officers and crew extended excellent, courteous and cheerful cooperation throughout the trip ITINERARY The ship left the Terminal Island Navy Base of Long Beach, California, at 1600 hours on the 12th of December and headed west- northwest to about 37°N by 123°W. It then turned east-southeast and moved into the area around 31°30'N by 118°00"W where it remained on maneuvers until 19 December when it returned to Long Beach with a short stop at Seal Beach on the 20th (See TABLE I). The area of maneuvers will hereafter be referred to as the Grid (See FIGURE I). A total of 76.1 hours and approximately 694+ miles of diurnal and 2.5 hours and 42+ miles of nocturnal observations was concluded (See TABLE II). Since mileage estimates are unreliable due to the