Abstract: A cable brake and lock device to control the release of a mooring cable crises a spring-biased piston abutting an elastic brake element, with the cable passing through both. An initial, preselected force is applied by the spring to the piston and the brake element, causing the element to lock onto the cable. When the force of the ambient, hydrostatic pressure exceeds that of the spring, the spring is compressed, releasing the piston from the elastic brake element to permit the cable to run freely. Any decrease in the ambient pressure will permit the piston to again contact the brake element to lock the cable.