A system includes a first jacket that contains seawater and a first tank storing a first fluid under pressure. A second jacket contains seawater and a second tank storing a second fluid under pressure. An actuator cylinder defines a space that receives the fluids from the first and second tanks. The actuator cylinder includes an actuator piston that divides the space into a first volume for the first fluid and a second volume for the second fluid. A hydraulic cylinder includes a hydraulic piston configured to move and change an amount of hydraulic fluid in the hydraulic cylinder, wherein the hydraulic piston is fixedly coupled to the actuator piston. A buoyancy plug changes a position in connection with the amount of the hydraulic fluid in the hydraulic cylinder, wherein the position of the buoyancy plug affects a buoyancy of a vehicle.