Series of laboratory tests have been conducted to investigate the wave heights transmitted over vertical wall and composite breakwaters by wave overtopping. The ratio of transmitted wave height to the incident wave height was found to be best expressed with the following equation for ordinary shapes of breakwaters with the crown height of R above the mean water level:
　　HT/HI＝0.5×［1-sinπ/2α(R/HI＋β)］
where the factors α and β have the values of 2.0 and 0.1 through 0.5, respectively. The Fourier analysis of wave profiles transmitted behind a model breakwater revealed the re-generation of transmitted waves as the superposition of number of wave trains which have the periods of T, T/2, T/3, ... and propagate with the different celerities corresponding to their own periods.