Green’s Dictionary of Slang

a generic term for a typical private soldier in the British army.

1896		Regiment 25 Apr. 61/2: A hospital ward [...] is looked upon by ‘Mr. Atkins’ as the abode of ‘scrimshankers’ and schemers [...] Yes, friend ‘Atkins’ if you have cut your finger or blistered your heel you may treat yourself with some hope of success.
1901		Sydney Sportsman (Surry Hills, NSW) 16 Jan. 2/5: The British Tommies let themselves go in real Petticoat-lane style [and] now that the belated shilling-a-day Atkinses are gone [...] we may well look on our own swaddies with eyes of pride.
1916		J.N. Hall Kitchener’s Mob 61: The lineal descendants of the line Atkins, men whose grandfathers had fought in the Crimea.
1917		A.G. Empey Over the Top 128: It was Old Scotty’s great ambition to be a sniper or ‘body snatcher’ as Mr. Atkins calls it.
1923		J. Manchon Le Slang.