Recent studies of the hydrodynamic responses of Los Angeles-Long Beach Harbors to the effects of long period waves [conducted in 1967-68 for the U.S. Army Corps of Engineers, Los Angeles District (35 )] , showed that the basins had characteristic modal periods of oscillation, which could be excited, apparently, on rather rare and largely unpredictable occasions. Available field data for confirmation of the mathematical results were largely non-existent at the time and satisfactory correlations were greatly hampered. In the interim the development of the Southeast Basin, Long Beach Harbor, for the reception of fast container ships has led to more detailed study and measurement of the responses of this particular basin to long period waves. The purpose of this paper is to present some of the original theoretical results of the 1968 study and examine their correlation with data of recent acquisition. Their bearing upon the motions in surge and sway of ships moored within the Southeast Basin will also be examined briefly in the light of some simple measurements of ship motions.

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