When considering the wave‐height transmission capacity of a dense pile structure, the spacing between piles transverse to the wave front is of considerable importance, and it is upon this characteristic length that studies should be based, thereby permitting a comparison with the effects of longitudinal spacing of piles. The results of this series of model experiments indicate that the relative depth parameter, d/L, may be neglected in the comparison of various transmission capacities. A maximum damping of waves resulting in a wave transmission of 42 pct of the incident wave height was obtained with a relatively dense configuration of 48 rows of ⅜‐inch‐diameter cylinders rectangularly arrayed and spaced one inch center‐to‐center. It was noted, within the limits of experimentation, that increasing the number of rows by 100 pct resulted in an average decrease in wave transmission of only 18 pct, irrespective of the density and configuration of the cylinders. Progressive wave‐height measurements through a dense cylinder configuration (rectangular array with one‐inch center‐to‐center spacing) showed that between 40 and 80 pct of the total decrease in wave transmission occurs within the first ⅕ of the length of the structure. More generally, it may be stated that approximately 50 pct of the total decrease in wave transmission occurs within the structure a distance, from the seaward face, of less than ¼ of the wave length. The overall results of the experiments show rather conclusively that a moderately dense piled structure is highly selective in its capacity to reduce wave action. Its ultimate transmission capacity for a given test section depends upon the magnitude of the incident wave steepness.