World War II: The Japanese imperial submarines I-21 and I-24 shell the Australian cities of Sydney and Newcastle.

I-21 (伊号第二一潜水艦, I-gō Dai Nijū-ichi sensui-kan) was a Japanese Type B1 submarine which saw service during World War II in the Imperial Japanese Navy. She displaced 1,950 tons and had a speed of 24 knots (44 km/h). I-21 was the most successful Japanese submarine to operate in Australian waters, participating in the attack on Sydney Harbour in 1942 and sinking 44,000 tons of Allied shipping during her two deployments off the east coast of Australia.