"Manned submersibles are vertical probes where mission times rarely exceed 12 to 14 hours and require mother ships on site to tend to them and their crews. There are only four manned submersibles in the world that can dive to a test depth of 20,000 feet, or slightly deeper. Two are Russian, with France and Japan having one each. Japan's Shinkai 6500 is currently the world's deepest diver at 21,300 feet. This exclusive club will soon be joined by the Chinese who are completing a 23,000-foot-capable manned vehicle. It should be in service by 2009-10. The titanium pressure hull was built in St. Petersburg, Russia, while other construction work and assembly are being done at Harbin, China.