query: What is the biggest icebreaker ship in existence?
passage: Nuclear-powered icebreaker
The icebreakers have also been used for a number of scientific expeditions in the Arctic. On August 17, 1977, Arktika was the first surface vessel in the world to reach the North Pole. Since 1989, some icebreakers have been used for Arctic tourist cruises.
passage: Polaris (icebreaker)
While all Finnish state-owned icebreakers survived the war, Finland had to hand over its newest and most powerful steam-powered icebreakers to the Soviet Union as war reparations. The rebuilding of the icebreaker fleet began in the early 1950s with the commissioning of the diesel-electric "Voima", the first icebreaker in the world to feature two bow propellers, in 1954. She was followed by two more icebreakers before the end of the decade to replace the steam-powered pre-war icebreakers now deemed obsolete, four in the 1960s to answer to the demands of the growing foreign trade, and finally three in the 1970s to keep all Finnish ports open through the winter.