Abstract: This disclosure includes systems and methods for actuation of subsea hydraulically actuated devices. Some systems use or include one or more subsea reservoirs, each having a body defining an interior volume configured to contain a sub-ambient internal pressure, the body defining an outlet in fluid communication with the interior volume, and a hydraulic power delivery system including one or more subsea valves configured to selectively allow fluid communication between the outlet of at least one of the reservoir(s) and a first port of the hydraulically actuated device. In some systems, the hydraulic power delivery system includes a rigid sliding member configured to unseal a selectively sealed outlet of at least one of the reservoir(s). In some systems, the subsea valve(s) are configured to alternatively allow fluid communication between the outlet of the at least one of the reservoir(s) and the first or a second port of the hydraulically actuated device.