How deep will a modern submarine go?

The Los Angeles class submarine has an operating depth of "greater than 800 feet" according to official releases. It doubtless goes a bit deeper. Some Russian boats, with their super tough titanium hulls (as opposed to the steel hulls of the US Navy boats and other Russian boats) can go deeper. How much deeper? The Russians are a little tight-lipped about that. Most think that depths in excess of 3,000 feet were easily accomplished, and one report suggested that 4,000 feet was within the reach of these vessels. People don't really talk much about that kind of stuff. As you might guess, the information is classified. Submarines are considered to be "self-sufficient" and able to operate for extended periods without support vessels. This differentiates the submarine from the submersible. Let's just look at those a moment.

Submersibles, which are not "true" submarines, operate independently from support vessels. With these civilian or research craft, the depths involved would be greater than with submarines. The Trieste reached a depth of 10,900 meters, or more than 35,000 feet when it dove the Pacific's Challenger Deep, the deepest spot in any ocean. The Alvin, the submersible that first dived the Titanic, can reach depths of 4500 meters. Alvin's replacement will be capable of reaching 6500 meters.