Green’s Dictionary of Slang

(Aus.) a German.

1919		E. Dyson ‘Bricks’ in ‘Hello, Soldier!’ 31: It was fare-the-well to Herman with a bullet through the bone.
1974		(con. WWII) E.H. Hunt Undercover 23: At least once a week we would come across [...] a German sailor’s corpse. These we would [...] search for documents before returning ‘Herman the German’ to the deep.
1947		D. Davin For the Rest of Our Lives 227: So up come the bloody Hermans.
1959		(con. 1940s) G. Slatter Gun in My Hand 56: Silly sods said Evan, that sort of thing gives us a bad name with the Hermanns.
1968		(con. 1940s) G. Slatter Pagan Game (1969) 71: Ridiculous slogans like [...] Hermann is Vermin.