The U.S. Navy's sophisticated "Bluefin-21" was launched Monday from the Australian navy ship Ocean Shield to search a relatively small section of the Indian Ocean floor, some 2.8 miles beneath the ocean’s surface. However, AUV was only able to complete six out of 16 scheduled hours of searching in its debut. It exceeded a 14,763-foot depth limit and a built in safety feature forced it to return to the surface, officials said.