Green’s Dictionary of Slang

(orig. milit.) cheap white wine; thus vongrooge n., cheap red wine.

1918		B.E.F. Times 22 Jan. (2006) 280/1: Owell then get some old vang blang!
1919		C.H. Thorp Handful of Ausseys 217: ’Ad some wine — vin blong.
1919		W.H. Downing Digger Dialects 52: von blink — A humorous corruption of vin blanc.
1922		D. Mackenzie Sixth Gordons in France and Flanders 56: True, they did not know much of the language beyond ‘Bon jour,’ ‘pang’ (bread ), ‘vin blong’ (white wine), and ‘oof’ (egg).
1924		(con. WWI) A.G. Pretty Gloss. Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: vin blank. White wine see Point Blanc.
1929		(con. WWI) H. Odum Wings on My Feet 214: Go out try to buy French wines, dam’ vin blank, red gin, rum [...] jes’ anything we could git, if would git alcohol behind eyes.
1931		(con. WWI) V. Tilsley Other Ranks 12: Abbeville, me lads. Abbeville, hundreds of miles out of this, and a pay parade tomorrow. Vin blong and egg and chips till you bust.
1933		(con. WWI) F. Richards Old Soldiers Never Die (1964) 83: Ving blong was very cheap [...] a man could get a decent pint and a half bottle for a franc.