Initially weighing slightly more than water, the craft descended 10.9 km (6.77 miles) below sea level. At the bottom, the pellets were ejected, and the buoyant gasoline floats carried Trieste back to the top. This feat has never been replicated by a manned craft, although several unmanned submersibles have since explored the Challenger Deep.
The deepest-diving large, military-style submarine was the Soviet submarine K-278 Komsomolets, with a hull made oftitanium, making it very expensive, but able to withstand significantly deeper dives than the best submarines made of high-grade steel, like American nuclearsubmarines. The Komsomolets was anuclear powered submarine specially designed to make trips as far down as 1300 meters (4265 feet) below sea level, definitely less than the Trieste, but very significant because the Komsomolets had to "defend" a much larger air bubble against the encroaching pressure of the surrounding ocean.
Compared to the best American nuclearsubmarines, of the Seawolf class,Komsomolets had about 78% better diving capabilities. Seawolf submarineshave an estimated crush depth of about 2400 feet (730 m). The Seawolfsubmarines are constructed of a high grade steel called HY-100, capable of withstanding 100 atmospheres of pressure. As a rule of thumb, the pressure increases by one atmosphere for every 10 m of descent
http://www.wisegeek.org/what-is-the-deepest-depth-a-submarine-can-go.htm
Deep sea exloration versus space exploration comes down to one issue above all else. How to accomplish deep sea exploration in a manner that doesnt disturb or destroy fragile deep sea ecosystems.. not because we are afraid of being eaten by a Megladon or some unknown monster..
RELEASE THE KRAKEN!
