Green’s Dictionary of Slang

(orig. UK milit.) a lance-corporal.

1896		‘Army Slang’ in Regiment 11 Apr. 31/2: A lance-corporal is a ‘Lance Jack’ and his stripe [...] is the ‘dog’s elbow’.
1915		F. Garrett diary 15 July 🌐 Bob GARDINER wants to be transferred to a troop, not being able to tolerate the Lance Jack.
1916		J. Hargrave At Suvla Bay Ch. xxiv: One of my ‘lance-jacks’ (lance-corporals) had been missing for a good long time.
1929		(con. 1916) F. Manning Her Privates We (1986) 29: That bugger takes me for a bloody lance-jack.
1941		G. Kersh They Die with Their Boots Clean 85: I run into him the other day, and he’s a lance-jack.
1959		G. Slatter Gun in My Hand 184: He was only a lance-jack.
1968		P. Terson Apprentices (1970) I i: He ended up a punch drunk lance-jack in the Burmese jungle.
1974		D. Ireland Burn 6: Every tinpot lancejack talks about the digs.