(chiefly Australia, informal, uncountable) Military national service, conscription.
(chiefly Australia, informal, countable) A person doing military national service.
2009, Raja (Arasa) Ratnam, The Dance of Destiny, page 166,
[…] an English acquaintance. He had been one of the national servicemen from the UK stationed in Malaya, and had had his share of duty on the night train. He explained that many of his ‘nasho’ colleagues were sensibly afraid of being shot at.