Abstract: A hydraulically actuated fast action gate valve for gating highly viscous uids in a salt water environment includes front and back plates having openings for connection to conduits containing the viscous fluid and a center plate having a slot for receiving a slidable gate that includes an optional check valve. A gate is positioned within the slot and includes upper and lower grooves that provide rapid equalization of pressure of the viscous fluid between the opposite ends of the gate when the gate is rapidly actuated. One end of the gate is connected by a locking pin to an actuating rod that is driven by a hydraulic cylinder that is mounted external to the valve. The front and back plates have opposing passages allowing the actuating rod to be secured to the gate so that the hydraulic cylinder may be removed. An optional opening is provided in the back plate to permit the introduction of a non-gated fluid into piping contained within the inlet conduit.