A control rod drive system for a nuclear reactor that employs hydraulic cylinders to operate a conventional plunger/gripper drive system to incrementally move control rods into and out of the core of a reactor. The pressure differential for driving hydraulic pistons within the cylinders is obtained from the difference in pressure between the outside and inside of the core barrel of the reactor and control of the pistons is obtained from external solenoids attached to the reactor control system. The external solenoids regulate a charging pump feed to Poppet valves that control the hydraulic feed to the cylinders. A hydraulic piston/cylinder drive is also provided for the shutdown rods which operate in either an all in or out of the core condition.