The first of two Russian mini-submarines that traveled to the Arctic Ocean floor at the North Pole has returned to the surface, the ITAR-Tass news agency reported. The second mini-submarine is still coming back to the surface. Expedition organizers said the greatest risk facing the six crew members, three on each vessel, was being trapped under the ice and running out of air. Each sub had a 72-hour air supply. The Mir-1 spent about 40 minutes near the surface before it found a patch of sea surface free of ice, ITAR-Tass said. In a perilous project mixing science, exploration and the scramble for potential oil and gas fields, crews of the Mir-1 and Mir-2 were engaged in what Russian authorities called the first dive to the ocean floor at Earth's northernmost point. The crew of the Mir-1 dropped a titanium capsule containing the nation's flag on the bottom, symbolically claiming almost half of the planet's northern polar region for Moscow. "It was so good down there," Chilingarov, 68, a famed polar scientist, said after coming back. "If someone else goes down there in 100 or 1,000 years, he will see our Russian flag."