Green’s Dictionary of Slang

choco n.1

also chocko
[chocolate soldier n.]
(Aus.)

1. a militiaman or conscripted soldier, esp. one who was drafted into the WWII militia but never left Australia; also attrib.

[Aus]L. Glassop We Were the Rats xi: How do you feel about the chocos? And the munition workers?
[Aus]D. Stivens Courtship of Uncle Henry 26: [She] called out the militia guard. Guard came in at the double with fixed bayonets Nolan got up clenched his fists [...] says ‘Come on, you choco bastards, come on!’.
[Aus]S.L. Elliott Rusty Bugles II iv: andy: You big galah. [...] keghead: In your great dinger, you rotten crawling chocko.
[Aus]‘David Forrest’ Last Blue Sea v: Militiamen (Chocolate Soldiers, Chockos) were mostly wartime conscripts. [...] The Chock War, the bitter discord between the A.I.F. and the Militia, began in Liverpool Camp near Sydney in October 1939.

2. a conscientious objector.

[Aus]Cusack & James Come in Spinner (1960) 24: Hero be blowed. He’s a choco. Caught in the draft. They say her old man put the military on to him but she’s succeeded in keeping him in Melbourne so far.
[UK](con. 1940s) G. Dutton Andy 91: Your country called you and you came. Not a chocko amongst you.