France, Russia, and Japan currently operate the world's deepest-diving manned submersibles. The French Nautile and the two Russian Mir vehicles can dive to 20,000 feet (6,000 meters). Japan's Shinkai 6500 goes 1,600 feet deeper to be the deepest diver-that is, until the People's Republic of China (PRC) launches their newest submersible.
The deepest diving U.S. submersible is the Navy-owned Alvin at 14,764 feet. Operated by the Woods Hole Oceanographie Institution since 1964. active planning is now underway to build a replacement, with National Science Foundation funding, that can dive to 21,325 feet (6,500 meters). It is estimated that the $22 million project will be completed by 2009.
The importance of a 20,000-foot capability-when the oceans' maximum depth is about 36.000 feet-is that this depth choice offers excellent cost-performance tradeoff. A submersible with this limit can access about 97% of the world's ocean seafloor, even though the limit is only slightly more than half the ocean's maximum depth.