Before Nautilus, submarines had to surface, or at least extend a snorkel above the waves, to take in air needed to run their diesel engines and charge their batteries for electric propulsion. But running off a nuclear reactor meant that Nautilus needed to do none of these things. In fact, Nautilus had already been deep underwater for three days before it reached the Pole and did not come back to the surface, near the coast of Greenland, until 7 August 1958 – spending a week beneath the waves and ice.