Green’s Dictionary of Slang

bunker n.¹

beer.

1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1864, 1867, 1870		Hotten Sl. Dict.
1874		Kent & Sussex Courier 9 Dec. 6/1: One [...] accuses one of the pupil teachers (of the feminine gender) with writing a treatise on Swipes, Bunker or Cat-lip, and I must necessarily infer that she must have a proneness for getting Buffy and Kisky.
1900		Eve. Teleg. (Dundee) 1 Sept. 3/6: The language of the London East-end pub [...] ‘bunker’ and ‘heavy wet’ — Beer.