Abstract: A percussive rotational impact hammer assembly for creating high torques. A generally cylindrical piston rotatably mounted on a hammer inside an outer casing oscillates on the hammer and strikes an impact surface on the hammer. The piston and housing have pressurized fluid ports and passageways for conducting pressurized fluid to alternately load an impact-driving chamber and return chamber. The piston is accelerated against the impact surface and the kinetic energy of the piston is transmitted to the hammer transmitting the rotational movement to a member engaged with the hammer, such as a drill bit or other member. The rotational impact hammer assembly can be adapted for use in a downhole hammer, in break out tongs for drill pipe, in wrenches for loosening or tightening nuts and bolts, or in other mechanical devices where high torque is desired.