Manned submersibles are vertical probes where mission times rarely exceed 12 to 14 hours and require mother ships on site to tend 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 each having one. Japan's Shinkai 6500 is currently the world's deepest diver at 21,300 feet.
This exclusive club will be soon 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.
The United States no longer has this capability even though it was the founding member of the 20,000-foot club. When the Bathyscaph Trieste II was retired in the early 1980s, the Navy's Sea Cliff was converted from a 6,500-foot to a 20,000-foot vehicle. Then after the Sea Cliff's retirement in 1998 it was given to the Woods Hole Oceanographic Institution, which decided not to return it to service.