How long was MASH on the air?
The television series MASH aired from September 17, 1972 to February 28, 1983 an 11-year run.
M.A.S.H. the TV series was based on MASH the film which was based on the novel MASH: A Novel About Three Army Doctors written by Richard Hooker. However, if you mean mash as in mashed potato, then I'm certain that it was serendipitously invented/created when some unknown person boiled the potatoes too long, probably a few hundred years ago.