The U.S. National Grid (USNG) system is based on and interoperable with the Military Grid Reference System (MGRS). The main difference is the 100,000-meter grid two-letter identification. The USNG lettering scheme is identical to the MGRS 100,000-meter grid lettering scheme for the North American Datum (NAD83). USNG, however, uses the same 100,000-meter lettering scheme for both NAD83 and NAD27, whereas MGRS has two lettering schemes for quick identification between the datums. USNG coordinates indicate that the coordinates are in the NAD27 datum by appending "(NAD27)" to the end of the coordinate, for example:
The Washington Monument (USNG):
18S UJ 2348 0647 [NAD83 is implied]
18S UJ 2345 0626 (NAD27)
For more information on the U.S. National Grid, please visit Introducing the United States National Grid or www.fgdc.gov/usng.