On 1 July 1954 the U.S. adopted the the International Nautical Mile in lieu of the U.S. Nautical Mile.
Miles derived from the length of a degree of an Earth meridian — called nautical miles, meridian miles, geographical miles, or sea miles — go back thousands of years. They have had many values, typically based on 10, 12, 15, or 60 miles to a degree of a great circle. The British and U.S. nautical miles were each derived by taking 60 nautical miles per degree, but their values were nevertheless not the same.
In 1929 the International Hydrographic Bureau obtained an agreement from a large number of countries to adopt a value of 1852 meters for the nautical mile, the unit thus defined to be called the International Nautical Mile. However, a few countries, including the U.S., chose not to accept the new value.
In 1953 the Department of Defense and Department of Commerce considered and adopted a proposal to switch to the new value for the nautical mile. Officially, as of 1 July 1954, the nautical mile in the U.S. was defined to be 1852 meters, replacing the previous value of 1853.248 meters. (The “old” U.S. nautical mile had also been defined in terms of meters ever since the Mendenhall Order of 1893, although that order rounded the value to 1853.25 m.)
For more details, read the 1954 NBS announcement of the adoption of the International Nautical Mile.
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This page prepared by USMA member Gary Brown.
Updated: 2009-06-13