Abstract: A submersible work vessel and a method of using the same are disclosed. The vessel contains an internal work space. It also contains a set of openable jaws that are designed to engage an underwater pipe. When the pipe is engaged, it will pass through the internal work space of the submersible work vessel. When the jaws have engaged the pipe, the internal work space should be substantially watertight, at which point the water in internal work space may be pumped out. When the water has been substantially evacuated, a worker may enter the internal work space and work on the pipe. One of the principal tasks the work vessel is designed to facilitate is the installation of a blow out preventer. The worker will install the blow out preventer on the pipe. The blow out preventer is designed to remove a section of the pipe and then to seal the severed pipe. This is preferably done with a cutter mounted on a hydraulic arm and a sealing block also mounted on a hydraulic arm.