This report describes a model water tunnel built in 1928 to investigate the possibility of using water tunnels for aerodynamics investigations at large scales. The model tunnel is similar to an open-throat wind tunnel, but uses water for the working fluid. Results are given of tests of the tunnel and also of some observations made with model airfoils in the tunnel to study the phenomena of cavitation. It is concluded that a water tunnel does not offer a convenient method of making aerodynamic investigations at large scales. A large diameter water tunnel would be of value chiefly for use in the study of cavitation.