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A unit of distance. The nautical mile, or sea mile, is used primarily in navigation. Nearly all maritime nations have adopted the International Nautical Mile of 1,852 meters proposed in 1929 by the International HydroGraphic Bureau. The U.S. departments of Defense and Commerce adopted this value on July 1, 1954.

Using the yard-meter conversion factor effective July 1, 1959, (1 yard = 0.9144 meter, exactly), the International Nautical Mile is equivalent to 6,076.11549 feet, approximately. The geographical mile is the length of 1 minute of arc of the equator, considered to be 6,087.08 feet. The statute mile or land mile (5,280 feet in the United states) is commonly used for navigation on rivers and lakes, notably the Great Lakes of North America. See also cable, measured mile.

In British usage, a sea mile is distinguished from a nautical mile. A British sea mile equals the distance of covered by 1' of latitude, exactly, or any 1' arc on a great circle along the earth's surface. In practical navigation we tend to equate nautical miles with sea miles but they are not exactly the same.

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