KISS is a design principle first noted by the U.S. Navy in 1960. First seen partly in American English by at least 1938, KISS implies that simplicity should be a design goal. The phrase has been associated with aircraft engineer Kelly Johnson. The term "KISS principle" was in popular use by 1970. Variations on the phrase include "keep it simple, silly", "keep it simple and straightforward", "keep it simple, soldier", and "keep it simple, sweetie".