An ultrasound probe includes a transducer array which is moved back and forth to sweep the image plane of the array through a volumetric region for 3D scanning. The transducer array is mounted on a carriage assembly which moves back and forth on a pair of rails inside a fluid compartment in the probe. The rails are preferentially arcuately curved to provide an elevationally divergent scan with a relatively wide aperture in the near field. A cam is provided for a motor-driven cable drive for the carriage assembly which provides relatively linear motion through the path of travel of the transducer array.