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  3. The development of ravel under the oceans For millennia humans have been intrigued by what lies beneath the sea, and althoug

The development of ravel under the oceans For millennia humans have been intrigued by what lies beneath the sea, and althoug

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问题             The development of ravel under the oceans
    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 maneuvering,  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 Henley—named after its financier rather than its inventor—sank twice during training missions with 11 crew members losing their lives including Henley himself. Notwithstanding these failures, it was commissioned again in 1864 to attack 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 recognized but there still remained the challenge of operating safely under the water.

    The US Navy could appreciate the strategic benefits of having submarines in its fleet and held a competition to encourage design and construction of these underwater craft. The inventor, John Holland, won the competition and it was his sixth prototype, the Holland, that the navy bought and added to its fleet in 1900.  This  submarine was  quite different  from previous  designs.  It was propelled by a gasoline engine that turned a propeller while the vessel was on the surface. When it submerged, the engine ran a generator to charge batteries to  operate  an  electric  motor.  The  improved  propulsion  methods  were, unfortunately, highly dangerous. Not only is gasoline flammable and unstable, using it in the restricted environment of a submarine posed quite a hazard for the crewmen. There was another problem too: the batteries were not only heavy, cumbersome and inefficient but they were also extremely volatile.
    During the same period  as Holland’s efforts were being trialed,  a German scientist by the name of Rudolf Diesel, created an engine which used fuel less explosive than gasoline and which could consequently be stored safely. Another advantage was that there was no necessity for an electric spark to ignite the fuel. These safety improvements combined with better fuel economy allowed Diesel engines to power a submarine for longer on the surface;  however, batteries were still needed to supply energy for underwater operation.
    Although diesel-powered submarines were successful and used by the US Navy for almost 50 years, the search for a single power source carried on. It wasn’t long before the concept of nuclear power was realized in Germany and taken up by an American physicist, Ross Gunn, who could envisage it potential in submerse idles. A research team was put together to adapt the concept of nuclear power for use in submarines. In effect, modern nuclear submarines have on board small nuclear power plant which produces a great amount of energy. This is used to heat water and create steam which drives a huge turbine which turns the propeller.
    There have been many adaptations and technological  improvements made to submarines over they ears but the shape is basically the same. Obviously, it is a totally enclosed craft, cigar-shaped with narrowed ends. The outer hull is the largest part of the boat and forms the body. The inner hull is designed to resist the considerable water pressure and insulates the crew from the cold. This is where the crew works, eats and sleeps. It also contains the engine room and the apparatus that makes clean air and clean water. Between the hulls are the ballast tanks for controlling buoyancy. There is a tall fin-shaped sail that comes up out of the hull. Inside the sail is the conning tower and extending from this, to the fore, there is a periscope (through which the captain can see the sea and sky when the submarine is near the surface of the water). Sonar is used for navigation deep below the surface. The other projection from the conning tower is the radio antenna.
    Underwater, there are two controls for steering the submarine. The rudder(like a tail fin) controls side-to-side movement and diving planes influence rise and descent. There are two sets of diving planes: the forward sail planes and the stern planes, which are located at the back with the rudder and propeller.
    Advancing technology will undoubtedly result in different shapes and modes of operation and it is quite possible that, in the future, submarines will be manned by robots or computer technology that communicates information to land bases via satellite.
Questions 1-6
    Answer the questions below.
    Choose NO MORE THAN THREE WORDS from the text for each answer.
    Write your answers in boxes 1-6 on your answer sheet.
For what reason was Diesel’s fuel considered safer than Holland’s?
选项
答案less explosive/volatile
解析
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