We've written a step-by-step guide for getting both pre-1970 and post-1970 Service Records from the National Archives of Australia.
In 1970, the Navy computerised its personnel records.
Prior to 1970, Service Records were recorded manually on paper. All of those records have been scanned and can be viewed on the National Archives website.
From 1970 on, Defence switched to a computer system for managing Service Records. These records aren't on the web. You must ask the National Archives for the records and they, in turn, may have to request the records from Defence. The whole process is more complicated.