"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
Launched in 1954, the first nuclear powered submarine was the USS Nautilus. Nuclear power allowed submarines to operate at high speeds while staying underwater longer than other forms of propulsion such as diesel-electric.