Abstract: This invention pertains to a rotary disk tool which utilizes pressurized water as the working fluid. When an operator engages a trigger on a novel control handle and valve assembly, pressurized seawater enters the rotary disk tool through the control handle and valve assembly into a seawater powered vane motor. The shaft of the seawater powered vane motor, is coupled to a drive gear. The drive gear, in turn, is in operative engagement with a driven pinion coupled to an output shaft which drives an abrasive disk. Seawater exhausted from the motor into a gear and pinion housing provides lubrication for the drive gear, driven pinion, and the bearings used with the gear and pinion. The seawater is then exhausted from the housing as a fan spray directed onto the back of the abrasive disk so as to reduce drag of the disk in water and to flush away loose material from the work surface.