Green’s Dictionary of Slang

(Aus.) a soldier who is reluctant to fight.

1918		R.H. Knyvett ‘Over There’ with the Australians 134: We carried off the ‘championship cup,’ beating the ‘Chocolates’ by two or three points. We might not have been so elated had not the ‘Chocs.’ been such nuts on themselves, for they had been offering ten to one on their chances.
[1919		W.H. Downing Digger Dialects 16: chocs, the 8th Brigade (‘Tivey’s Chocolate Soldiers.’ Originally an abusive name; now an honourable appellation)].
1999		G. Seal Lingo 57: Although chocolate cream soldiers had been in use since the late 19th century in British parlance, Australians adopted it as their own, rapidly abbreviating it to chocs.