Green’s Dictionary of Slang

army rocks n.

[rhy. sl.; orig. grey woollen Army socks]

socks.

1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier.
1960		J. Franklyn Dict. Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.