Abstract: The jacking apparatus comprises a load frame adapted to move relative to a rail having single slots longitudinally spaced therealong. A pawl carriage is disposed inside the frame for movement relative thereto. A single, double-acting hydraulic actuator is coupled between the frame and the carriage. A pawl member is vertically supported by the carriage for pivotal movement between two diametrically-opposite positions. The pawl member has a claw foot shaped so as to fall into successive slots. The claw withdraws from a rail slot and permits linear motion of the carriage over a distance equal to the actuator stroke, near the end of which the claw falls into the next slot. The claw will then permit linear motion of the load frame during the opposite stroke of the actuator. The reciprocating strokes of the hydraulic actuator produce alternate incremental movements of the load frame and of the carriage.