Naval control, or control of the water, was important during 
World War I. Countries on both sides of the war expanded their navies and built huge battleships and submarines.
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Even bigger ships called aircraft carriers, which transported airplanes, were used for the first time at the end of the war.
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Today, the United States has developed the strongest navy in the world.
Why do you think modern U.S. leaders view having a powerful navy as being so critical?
