A submarine explodes 3,000 feet beneath the ocean's surface, sealing off the crew in a confined space. It's cold and dark, and oxygen supplies are running low. Pressure keeps the hatch closed, but even if it opened, the human body could never survive at this depth. The only thing to do is to wait for help from above.

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Stricken Canadian submarine HMCS Chicoutimi wallows in heavy seas as a salvage vessel moves into position. See more submarine pictures.

Fortunately this scenario isn't one that happens very frequently. Deep-sea rescue missions are few and far between because of the rarity of submarine disasters. Only a handful of countries even maintain deep-sea rescue operation capabilities. As a result, most missions are carried out on a multinational basis.

The Priz Rescue
In August 2005, the Russian submarine Priz became snared in underwater cables on the bottom of the ocean off the coast of Siberia. The sub was trapped, and the seven Russian sailors aboard the Priz faced certain death with their oxygen supplies running out and ­temperatures reaching lows of 43 degrees Fahrenheit (6 degrees Celsius). After a failed rescue attempt by a Russian Navy team, a distress call was sent out and the British Royal Navy was the first to respond.

Initially, it was thought that the minisub was caught in fishing nets. It was later found that the web of cable was part of an underwater surveillance antennae anchored to the sea floor. Using the unmanned Scorpio rescue sub, the cables were cut loose, freeing the sub after 72 hours on the ocean's floor. Military doctors were on hand to treat the men, all of which were in fairly good shape considering the peril they faced [source: BBC].

In this article, we'll look at the history of deep-sea rescue and the special equipment currently being used and in development. We'll also look at some of the training exercises, as well as efforts being made around the world to avoid submarine disasters.