Exploration of the ice‐covered ocean around the North Pole. The search for a north‐west and a north‐east passage from Europe to the Orient gave impetus to Arctic explorations from the 16th century onwards. The British geographer Sir John Barrow promoted explorations in the early 19th century, while an attempt by Sir John Franklin (1845) to find the north‐west passage led to his disappearance and ultimate confirmation of his death. The 40 or more search parties sent out after him brought back valuable information about the Arctic regions. In 1850 the British Arctic explorer Robert McClure completed a west–east crossing, but the first continuous voyage remained unachieved. In 1878–79 the Swedish Baron Nordenskjöld undertook the first traverse of the north‐east passage from Norway to the Bering Strait, but the north‐west passage was not completed until the voyage of the Norwegian Roald Amundsen in 1903–06. During the 20th century there have been many Arctic expeditions made by Soviet, US, and European scientists seeking ways to develop and exploit the region; a number of drifting observation stations have also been set up on ice floes. In 1968 oil was discovered in northern Alaska, and exploration for further Arctic oilfields has continued. The first vessel to cross the North Pole underwater was a US nuclear submarine, the Nautilus, in 1958 and in 1977 the Soviet icebreaker Arktika was the first surface ship to reach the Pole.