80 years after an unprecedented attack, Australia is having run-ins with another rival close to home

• In May and June 1942, Japanese submarines attacked the Australian cities of Sydney and Newcastle.
• The attacks were an intense reminder of the war moving closer to Australian shores.

In the early hours of May 29, 1942, a reconnaissance plane launched from Japanese submarine I-21 was spotted over Sydney Harbor. Observers believed it was an Allied plane and didn't raise the alarm.

The plane was in fact doing a final reconnaissance of the harbor for four other Japanese submarines, I-22, I-24, I-27, and I-29, which had arrived off Australia's coast carrying three Type A Kō-hyōteki-class mini-submarines on their decks.

On the night of May 31, the mini-subs were launched toward the harbor, where they delivered a message to Australians about the war inching closer to their homes.

Eight decades later, tensions in the Pacific are rising once again, and the surprise attack on Allied ships in Sydney is a reminder of the proximity of the threat Australia now faces.

A tense time

By May 1942, the war and its intensity were visible to Australians.

In December 1941, the Japanese dealt the British a devastating defeat by sinking the battleship HMS Prince of Wales and the battlecruiser HMS Repulse in the South China Sea.

In January 1942, Rabaul, in what is now Papua New Guinea, was captured by the Japanese, who turned it into a major base. February saw the Japanese capture Singapore and bomb the port city of Darwin in northern Australia. In early March, the Japanese captured the Dutch East Indies, which is now Indonesia.

Japan's advance was finally checked on May 8 at the Battle of the Coral Sea, which relieved some of the pressure on northern Australia, but Japanese air and submarine attacks were still a great threat.

Southern Australia was believed to be safer because it was far from the fighting, and early in the war Allied capital ships — such as battleships, cruisers, and aircraft carriers — tended to dock there, especially in Sydney Harbor.

At the time, Sydney was not optimally prepared for submarine attacks. There were no regular offshore sea or air patrols and the harbor's anti-submarine net was still under construction.

There were passive detection systems around the harbor entrance, but the Royal Australian Navy didn't have submarines or much experience hunting them, so its personnel didn't quite know what to listen for.

The Japanese Navy was keen to strike Sydney's target-filled harbor and decided to use mini-submarines rather than fleet submarines because their size increased their chances of getting in and out undetected. The cigar-shaped Type As were 78 feet long and 5 feet wide, had a crew of two, and were battery-powered. They were armed with two 770-pound torpedoes and carried scuttling charges.

Five Type As were used unsuccessfully at Pearl Harbor, but the Japanese believed that subsequent upgrades, including cages on the bow and conning tower designed to cut through anti-submarine nets, increased their likelihood of success.

Their targets were any Allied capital ships in Sydney Harbor, especially the heavy cruisers USS Chicago and HMAS Canberra, and the light cruiser HMAS Adelaide.

The raid

The three subs were launched at 20-minute intervals on the evening of May 31.

The first sub, M-27, entered the mouth of the harbor around 8 p.m. but got stuck in the completed section of the anti-submarine net. It was then spotted and attacked by two Australian navy patrol boats. M-27's crew detonated the scuttling charges to avoid capture, sinking the sub and killing themselves.

The second sub, M-24, had more success. It entered the harbor undetected around 9:48 p.m. but was eventually discovered and fired on by USS Chicago, which had been alerted by M-27's attempt.

M-24 fired its torpedoes at Chicago, but both missed. One ran aground but the other hit a seawall and detonated under the ferry HMAS Kuttabul. The explosion sank the ferry, killed 19 Australian and two British sailors, and slightly damaged a nearby Dutch submarine.

M-24 was hit by machine gun fire as it left the harbor and sank 3 miles off the coast north of Sydney. (It remained undiscovered until 2006.)

The third sub, M-22, entered the harbor after midnight. It was detected and Australian patrol boats pounced before it could attack. The patrol boats crippled the sub in one of the harbor's bays, and both submariners shot themselves.

The five Japanese fleet submarines spent two nights waiting for the Type As to return. On June 3, they left to hunt merchant ships in the area, attacking seven, sinking three, and killing 50 sailors.

On June 8, I-24 and I-21 returned and surfaced near Sydney. They bombarded the city and nearby Newcastle for 20 minutes with their deck guns, firing some 44 rounds before disengaging when coastal artillery returned fire.

Almost none of the Japanese rounds detonated and there were no casualties, but the attack further frightened the cities' residents.

A new, growing threat

The attacks on Sydney and Newcastle are reminders that distance alone won't protect Australia, especially against an enemy with significant air and naval resources. That has renewed relevance amid Australia's deteriorating relationship with China.

Canberra's call for an independent review of the origins of COVID-19 in April 2020 prompted intense backlash from Beijing. Since then, China has frozen high-level contacts and imposed trade restrictions on Australian goods.

There is also longstanding concern about China's influence in Australian society, and the tensions became a major issue in recent elections.

The situation has been made worse by recent incidents with the Chinese military around Australia.

On February 17, one of two Chinese warships sailing in the Arafura Sea between Australia and western New Guinea shined a laser at a Royal Australian Air Force P-8A Poseidon as it flew by on a patrol flight. Canberra condemned the Chinese crew's actions, calling it "a serious safety incident" with the "potential to endanger lives."

A military laser itself is not a weapon, but it is usually part of a weapon's fire-control system and is used to illuminate a target before firing. As such, lasing a ship or aircraft can be considered aggressive — the US has criticized China for similar actions in the past.

More recently, on May 13, Australia expressed concern about a Chinese intelligence-gathering vessel operating off its west coast, where it sailed by a secretive naval communications base. Peter Dutton, Australia's defense minister at the time, called it an "aggressive act" and said its intention was to "collect intelligence right along the coastline."

In recent years, amid rising tensions with Beijing, Australia has increased efforts to modernize its military and to strengthen its alliances with the US and others in the region — steps meant to counter a threat that will likely only grow in the years ahead.