Abstract: A threaded connection body (20) is welded to the outer surface of the wall (10) of a pipe, seachest or other flooded cavity (4) within the hull of a ship or floating off-shore installation. A sealed cutting apparatus (50) is mounted via a valve unit (30) on the connection body and a cutter extended through the open valve (34) to form an opening (18) in the wall (10). After retracting the cutter and closing the valve (34), the cutting apparatus is replaced by a sealed inspection unit (70) having a camera (71) which is extended through the valve and the opening to inspect the cavity (4). After retracting the camera and closing the valve, the inspection unit is replaced by a plug deployment unit (100) which is used to advance a plug (120) through the open valve and screw it into the connection body (20). The valve unit (30) can then be removed and replaced with a cap (90) so that the plug and the cap provide a double seal to the connection body.