Green’s Dictionary of Slang

a kilometre.

1915		E. Packe letter 22 Aug. 🌐 That Hooge show was rather good fun, we were watching the bombardment from our trenches about three Kilos away.
1917		A.G. Empey Over the Top 40: We marched eight kilos and then halted in front of a French estaminet.
1919		C.H. Thorp Handful of Ausseys 251: It’s fourteen kill-o’s from here to Bapaume.
1921		Dos Passos Three Soldiers 326: ‘How many kills is there to Paris, Yank?’ ‘Fifteen or sixteen, I think.’.
1929		(con. WWI) J.B. Wharton Squad 140: Up ahead a couple of kilos, I guess.
1932		(con. WWI) L. Mann Flesh in Armour 127: You might, if you liked, walk for five kilos westward to the little town.
1934		(con. WWI) G. Bruce ‘The Flaming Arrow’ in Goodstone Pulps (1970) 48/2: No experienced flyer would dare to penetrate eighty kilos behind the enemy lines.
1965		L. Haylen Big Red 101: The Fritzies could hear him I reckon kilos away.