It was a leading question replying to the statement by TheBlacksmith,
" And yet it was a joke because anyone with even the most basic knowledge of Japanese military equipment would have known that the Japanese could never have mounted a bombing raid on Melbourne. Their aircraft simply did not have the range. "
If you understand how the Japanese bombed Pearl Harbor, you can then understand how they could bomb Melbourne. As other people have pointed out, you use an Aircraft Carrier of which the Japanese had quite a few and they knew how to use them. Without doubt the Japanese had the capability to attack Melbourne and it would be unforgivable for the people responsible for Civil Defence not to prepare the Civilian population for such an event.
The Japanese attack on Pearl Harbour was not carried out by large bombers, they used dive bombers carrying a single large bomb and also ones carrying torpedos. The torpedos had been specially developed by the Japanese for the Pearl Harbour raid because the harbour was shallow, so they needed to be dropped at very low altitude then run quite shallow, otherwise all of them would have ended up in the mud.
Dive bombers and torpedos were fine armaments for use against ships, especially when they are conveniently lined up in nice rows like sitting ducks, but are practically useless against land based targets. Land targets require multiple medium weight bombs to do any good, and the Japanese had no aircraft of that type that could operate from carriers.
The attack on Darwin comprised dive bombers from the four carriers Kaga, Hiryu, Soryu and Akagi, the same four carriers that would be lost several months later Midway. The greatest devastation in Darwin came from Betty and Nell heavy bombers flying from land bases in Ambon and Celebes. And the attacks were almost totally undefended, we put up virtually no aircraft in defence and had virtually no effective anti-aircraft defence because their were no guns. What guns they had were useless due to an ammunition shortage.
The purpose of the raid on Darwin was to destroy the harbour and two airbases to prevent them being used by the Allies when the Japanese invaded Timor and Java.
Melbourne would have been a different target altogether, as there was no important airbases and the harbour was not a strategic asset. We did however, have significant war material factories at Fishermans Bend, Spotswood and Newport, but again they are targets that require larger bombers, dive bombers and torpedo bombers would not have been any use against those targets.