The shelling of Sydney and Newcastle by the Japanese submarines I-21 and I-24 represented a significant escalation in the conflict between Japan and Australia during World War II. Operating in the Pacific Theater amidst the increasing tide of Japanese military aggression, the submarines targeted the Australian mainland, illustrating the threat that Australia had begun to confront following Japan’s earlier successes in the region. The attacks commenced around dawn when the submarines commenced firing at installations, including oil tanks and other military targets, aiming to disrupt Australian defense capabilities and instill fear among the civilian population.

The I-21 and I-24 successfully executed their mission with some accuracy, hitting targets and causing limited damage. While there were no direct casualties from the shelling reported, the incident sent shockwaves through the Australian populace, marking a pivotal moment of vulnerability in a country that had previously seen itself as a safe distance from the battles of World War II. Local residents experienced the surreal sight of naval warfare within their urban shores, a stark reminder of the global implications of the conflict.

These attacks marked not only the audacity of the Imperial Japanese Navy but also a shift in Australian military strategy, as it became clear that Japan's aggressive push towards the south Pacific posed a real threat to Australian sovereignty. After the shelling, Australian Prime Minister John Curtin called for increased vigilance and military preparedness, urging his government to strengthen coastal defenses and reconsider national defense strategies. This event foreshadowed further military engagements and the establishment of more fortified defensive measures along the Australian coastline.