You could be forgiven for thinking that to answer this question, all you would have to do would be to look at the official Australian government UFO files and find the date of the earliest material.
The two earliest files related to 'flying saucers' as UFOs were called, in those days, discovered by the Disclosure Australia Project were:
(1) File series B5758 control symbol 5/6/Air Part 1 - dated from 21 Aug 1950. RAAF HQ Training Command.
(2) File series PP474/1 control symbol 5/5/Air - dated 29 Oct 1951. RAAF base Pearce, Western Australia.
So, we know that the RAAF had begun collecting material on 'flying saucers' at least from 21 Aug 1950.
In addition, in 1954 when he was preparing a report on flying saucers for the RAAF, Melbourne University physicist, Harry Turner (file series A703 control symbol 554/1/30 part 1) was given two files belonging to the Director of Air Force Intelligence. The date of the earliest report mentioned in Turner's report was from 1950.
It therefore came as a surprise when looking through digitised newspapers in the Trove collection of the National Library of Australia to come across the following:
"Melbourne - The RAAF has been investigating flying saucer reports since 1947, a high ranking officer revealed..." (Barries Miner (Broken Hill) Saturday 9 January 1954 page 5.)
" In Melbourne yesterday, a high ranking RAAF officer said that he personally believed 'objects seen in the sky over Melbourne have an interplanetary source.' The officer revealed that the RAAF had been thoroughly investigating flying saucer reports since 1947." (The Argus, Melbourne, Saturday 9 January 1954 page 5.)
So, did the RAAF commence investigating flying saucer reports as early as 1947, as the newspaper articles state? All we can say for certain is that none of the thousands of pages of RAAF or other government agency flying saucer/UFO files, supports a 1947 start date. That is not to say that the newspaper articles are incorrect, merely that the date of 1947 cannot be independently corroborated.