Subsea valves

A control valve apparatus adapted to be stationed in a subsea blowout preventer stack and used in connection with a production or drill stem test of an offshore well from a floating vessel, includes a valve section and a control section that are releasably connected together by a latch mechanism. The valve section has one or more fail-close valves for controlling the opening of the well, and the control section and latch mechanism are hydraulically operable for respectively actuating the valves and disconnecting the control section to enable its retrieval to the vessel leaving the valve section in place.