Grunt

US military slang for a low-ranking infantryman. It is thought to have originated during the Vietnam War, although some sources maintain from WWII. 'Grunt work' is lowly, labouring work, and this American expression dates from around 1900. It was an apt description for the sort of work that US infantry had to do in the frontlines during WWII or Vietnam, in sharp contrast to those who had cushier jobs at base headquarters.