Russian explorers have dived below the North Pole and planted a Russian flag on the sea floor. One Mir submersible reached the seabed first, followed by a second half an hour later. Each had three people on board. It is the first expedition of its kind. Oceanographers will use samples collected to study the sea bed. The aim is to stake a claim to oil and gas reserves in the Arctic. Expedition leaders were concerned about re-surfacing but both submersibles returned safely. Soviet and U.S. nuclear submarines have travelled under the polar icecap in the past, but no one has ever reached the seabed at the Pole before.