The U.S. Navy is sending unmanned vehicles to aid attempts to rescue seven crewmembers of a Russian mini-submarine trapped under the Pacific Ocean. The sub went down in 625 feet of water after snagging its propeller.

A Russian vessel reportedly was able to tow the small sub closer to shallow waters, but it has since lost contact. Oxygen levels in the craft have remained an object of speculation, with estimates ranging from 12 hours to several days.

The Russian mini-sub, designated the AS-28, is itself used to aid in rescue and salvage missions -- including the tragic 2000 sinking of the Russian nuclear submarine the Kursk, in which all hands were lost.

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