finestkind: I think the term digger as applied to gold miners went back earlier than Ballarat, right back to the mid 1800 gold rushes in Australia and New Zealand, but that is not military use.
That came later when it was sometimes, but not generally, used to describe both the New Zealand and Australian soldiers at Gallipoli.
However, my reading says that the first use of the term to an individual national unit came in 1916 when the New Zealand Pioneer Battalion were so called for their work digging trenches at the Somme.
"The Pioneers earned the nickname the 'Digging battalion' and the term 'Digger' was soon adopted by the rest of the New Zealand Division. By 1917 it had spread from the New Zealand Division to the Australian Divisions in the two Anzac Corps".
That quote is from New Zealand history, I accept that you might prefer to believe an alternative Australian version.
