Delft Hydraulics has performed an extensive investigation on the stability of rubble mound revetments and breakwaters under random wave attack. Two stability formulae have been derived which describe the stability of rock slopes as a function of wave height, wave period, slope angle, storm duration, permeability and damage level. The complete investigation is described in Dutch in the Delft Hydraulics Report M 1983. The investigation has further been described by Van der Meer and Pilarczyk (1987). In extension of the investigation on rock slopes Delft Hydraulics has set-up an investigation on the stability of artificial armour units. The first part of this investigation concerned the stability of breakwaters armoured with Cubes and is described by Van der Meer (1986). The second part was focussed on stability of Tetrapods and is described by Van der Meer (1987). Cubes were chosen as these elements are bulky units which have good resistance against impact forces. Tetrapods are widely used all over the world and have a fair degree of interlocking. ACCROPODE (R) can be regarded as the latest development, showing high interlocking, strong elements and a one layer system. Therefore, the ACCROPODE (R) was chosen to be investigated next. The study was partly financed by SOGREAH, France and partly by Delft Hydraulics as an internal research project.