Abstract: A subsea riser disconnect assembly 10 may be actuated from a drilling rig DR by axial movement of an upper riser 35 relative to a lower riser 28, for disconnecting the upper riser 35 from the lower riser 28. A subsea riser valve assembly 20 may be actuated from the drilling rig DR by axial movement of the upper riser 35 relative to the lower riser 28, for sealing an interior portion of the lower riser 28 and well bore WB below the subsea riser valve assembly 20. A drill pipe disconnect 30 may be actuated from a drilling rig DR, either onshore or offshore, for disconnecting an upper portion of drill pipe 236 from a lower portion of drill pipe 240. The drill pipe disconnect 30 may be actuatable by hydraulic and/or mechanical forces applied to the drill pipe disconnect 30 from the drilling rig DR. The drill pipe disconnect 30 may be compatible for use with or without the subsea riser disconnect assembly 10 and/or the subsea riser valve assembly 20.