The circumference of the Earth at the equator is 24,901 miles. The Earth is an oblate spheroid – meaning it is roughly a sphere but with slightly flattened poles. If you convert 24,901 to kilometres, you get 39,841 and change. Is it possible that you meant to write kilometres instead of “nautical miles”?

For what it’s worth, there is also a subtle difference between “1 mile” and “1 nautical mile”. 1 mile is defined as 8 furlongs, where a furlong is 220 yards, thereby giving “1 mile” a length of 1,760 yards, or 5,280 feet. By contrast, “1 nautical mile” is defined as 1 minute of latitude at the equator, where latitude defines east-west, not north-south. In angular measurement, there are 60 minutes in one degree [and 60 seconds in one minute]. That means that the Earth’s circumference would be divided in to 21,600 nautical miles [60 minutes x 360 degrees]. Because there are fewer nautical miles than miles spanning the circumference of the Earth, this means that 1 nautical mile is 6,080 feet, not 5,280 feet.

Largely unrelated [except to underscore the difference between miles and nautical miles] the historic marine measure of depth is not feet but fathoms, where one fathom equals 8 feet of depth. Consequently, there are 760 fathoms in one nautical mile of vertical depth.