填空题
For millennia humans have been intrigued by what lies beneath the sea, and although sub-marine travel was attempted from time to time, it did not become commonplace until the middle of last century. Several clever and innovative people had experimented with designs for submersible boats before then, but there was much loss of life and little success.
There had long been use of a primitive diving bell for explorative purposes but it was as a war machine that the submarine came into its own. The first development in the history of American submarines was a small submersible with a hand-cranked screw-like oar and a crew of one. It was built before the American Revolutionary War (1775-1783) but was adapted for use against the British during this war. Although its pilot twice failed to fasten explosive devices to British ships before losing control of his vessel, he escaped harm.
In 1800, an American inventor, Robert Fulton, designed an underwater machine that he called the Nautilus. His version brought in features that can still be found in some modern submarines, notably adjustable diving planes for better underwater manoeuvring, dual systems of propulsion, and a compressed air system that allowed it to stay down for about four hours without surfacing.
Development of submersible vessels lagged a long way behind the continued progress in the design of surface ships until the American Civil War (1861-1865) when both sides tried out various designs. One of those, called the Hunley—named after its financier rather than its inventor—sank twice during training missions with ii crew members losing their lives including Hunley himself. Notwithstanding these failures, it was commissioned again in 1864 to attack a ship in Charleston Harbor. A torpedo was used to strike and scuttle the ship—a first in naval history—but the submarine never reappeared and once again the whole crew perished. Its potential had been recognised but there still remained the challenge of operating safely under the water.