A hydraulic actuator includes a pneumatic piston, a hydraulic piston, and an engine valve on a common shaft. The pneumatic piston is urged between first and second stable positions primarily by a double acting pneumatic spring, with high pressure hydraulic fluid connected to a first hydraulic chamber being used to cock the hydraulic piston in a first stable position (engine valve closed). Hydraulic fluid isolated in a second hydraulic chamber is used to latch the hydraulic piston in a second stable position (engine valve open). Transfer of hydraulic fluid between first and second chambers is effected by a carrier for two check valves, which carrier in a first position disables the second check valve to permit fluid to flow from the second chamber to the first chamber, whereupon the first check valve closes (cocking). In a second position the carrier disables the first check valve to permit fluid to flow from the first chamber to the second chamber, whereupon the second check valve closes (latching). The carrier may be controlled directly by an EM actuator, or by hydraulic fluid channeled from a pilot valve which is EM actuated.