Abstract This paper describes water-tunnel investigations into the mechanics of “fixed”-type cavitation and into the probable mechanism through which this type causes material damage. High-speed motion pictures were used to study the cavity mechanics, and indications of the damage pattern were obtained by measuring the pitting rate on soft aluminum test specimens. Information was obtained on the frequency and intensity of the damaging blows, the distribution of damage in relation to the area covered by the cavitation, and the variation of the intensity of cavitation with velocity.