The launch of the American Nautilus nuclear submarine in April 1954 marked the beginning of the nuclear-powered ship era. Since then, the United States, Russia, the United Kingdom, and France have built a large number of nuclear submarines and numerous nuclear aircraft carriers, nuclear destroyers, and nuclear cruisers, with more than 300 currently in service. China has also built several nuclear submarines. After more than half a century of development, nuclear-powered vessels have become an important force in the navies of various countries, achieving a status unmatched by other types of ships in terms of strategic position and technological sophistication. For example, the Nautilus made the first human voyage beneath the Arctic ice in August 1958; the American Trident-class submarine can carry 24 missiles—each with eight nuclear warheads—has a submerged speed of 24 knots, and can sail continuously for 1.8 million kilometres on a single fuel load, remaining submerged for up to ten years without surfacing; the American carrier Enterprise and cruiser Long Beach circumnavigated the globe without docking or resupplying; and the Russian Komsomolets submarine dived to 1020 m in August 1984 and successfully launched a deep-sea torpedo at 1000 m depth.