Darwin has a habit of being flattened.
Particularly with major cyclones in the late 1800's, 1937 and 1974.
Then the Japanese in 1942/43. There were around 70 more raids into northern Australia after the first one. The Japanese also raided Broome and Exmouth to the far west and up to 300km south to Katherine.
The object was to deny the Allies a base in the region.
As I understand it, the Japanese Navy wanted to invade Australia but the Army wasn't so keen. Nevertheless, a fair deal of contingency planning seems to gone into the possible invasion.
A friend of my father was a Lt Col in the occupation forces and once dined with an official who claimed to have been the Mayor-designate of Melbourne had the invasion gone ahead. The chap had a very detailed knowledge of Melbourne, even knowing the number of the tram that ran past the Col's front door at home.
The Spitfires didn't arrive in Darwin until February 1943. Until then, we relied on the USAAF's P-40s for air cover.
The Spits were fairly evenly matched in results with the Zero, with both sides drawing blood. On the occasion the JAAF dropped by with an Oscar escort, several Oscars were lost with no losses for the Spits.