M81

English Etymology From M (used for en model) + 81 (short for 1981, the year of its introduction), following the pattern of the Model designation for U.S. military equipment.en 25 April 2021 Rifleman Q&A: How Do Army 'M' Numbers Work? w:American Rifleman https://web.archive.org/web/20210729155109/https://www.americanrifleman.org/content/rifleman-q-a-how-do-army-m-numbers-work/ Fairfax, Va. w:National Rifle Association The methodology of determining the Model designation for U.S. military equipment was easy until the late 1920s. Prior to that time, the year in which an arm was adopted was the Model designation. Noun - en military slang The woodland camouflage pattern used by the United States Armed Forces from 1981 until 2012. References Further reading U.S. Woodland