The Japanese attack on Sydney Harbor on the night of May 31 and the early hours of June 1, 1942, was a daring and audacious naval operation that brought the realities of World War II directly to Australia’s shores.

Utilizing midget submarines, the Japanese aimed to strike a significant psychological blow against the Allies by targeting naval vessels within the harbor, resulting in the tragic loss of 21 sailors aboard the HMAS Kuttabul.



World War II was a truly global conflict, but the Pacific theater played a unique and critical role due to its vast distances and the strategic importance of its island territories and sea routes. Following the attack on Pearl Harbor in December 1941, Japan rapidly expanded its territory across East Asia and the Pacific, seeking to secure resources and establish a defensive perimeter against counter-attacks from the Allies.

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Australia, being geographically situated close to the Pacific theater, became a pivotal base for Allied operations. Its proximity to Southeast Asia and the Pacific islands made it a crucial point for launching counter-offensives against Japanese forces and for providing logistical support.

The country also served as a refuge and a base of operations for forces from other Allied nations, including the United States, which were regrouping after setbacks in the region.

The crews of the Midget submarines at the attack on Sydney Harbor.

By 1942, the Japanese advance seemed unstoppable, and there was a genuine fear among the Allies that Australia itself could be invaded or isolated. The fall of Singapore in February 1942 and the bombing of Darwin, also in February 1942, starkly highlighted Australia’s vulnerability to Japanese attack.

These events underscored the strategic importance of protecting Australia and its surrounding waters to maintain a base for Allied counter-attacks and to prevent Japan from gaining further control of the Pacific.

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For Japan, the extension of its defensive perimeter and the severing of communications and supply lines between Australia and the United States were critical strategic objectives. By targeting Sydney, a key naval hub, Japan aimed to demonstrate its reach and capability, hoping to intimidate the Allied forces and perhaps force a reconsideration of their strategy in the Pacific.

The attack was meant to be a show of force, projecting Japanese naval power directly into what was considered a relatively secure Allied area.

Prelude to the Attack

The Japanese Navy’s intelligence-gathering efforts were a key component of their strategy in the Pacific. Recognizing the importance of Sydney as a naval base and its role in the Allied supply chain, the Japanese sought detailed information on harbor defenses, ship movements, and potential targets.

This intelligence was gathered through a combination of methods, including reconnaissance flights and submarine patrols. These efforts were not only aimed at Sydney but were part of a broader intelligence-gathering operation across the Pacific, intended to identify vulnerabilities in the Allied defenses.

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In the weeks leading up to the attack, the Japanese conducted several reconnaissance flights over Sydney Harbor. These flights were carried out by floatplanes launched from cruisers located off the Australian coast, which flew at high altitudes to avoid detection.

The information gathered during these flights provided the Japanese with a clear picture of the harbor’s layout, the positioning of anti-submarine nets, and the location of potential high-value targets. This aerial reconnaissance was critical in planning the attack, allowing the Japanese to refine their strategy and choose their targets with precision.

In addition to aerial reconnaissance, the Japanese utilized their submarines to perform close surveillance of Sydney Harbor and its approaches. These submarines patrolled off the coast, collecting data on shipping movements and naval activity. This information was crucial for understanding the patterns of Allied naval operations and identifying the best time and method for launching the midget submarines into the harbor.

The decision to launch an attack on Sydney Harbor was based on the accumulation of intelligence that indicated the potential for significant disruption to Allied naval operations. The Japanese command believed that a successful raid, even if it did not result in the sinking of a large number of ships, would have a psychological impact on the Allies and demonstrate the reach of the Japanese Navy.

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This decision was also influenced by Japan’s broader strategic objectives in the Pacific, aiming to project power, intimidate the Allies, and possibly force a strategic rethink of their operations in the region.

Armed with detailed intelligence from their reconnaissance efforts, the Japanese meticulously planned the attack. The choice to use midget submarines was influenced by the need for stealth and the desire to penetrate the harbor’s defenses undetected.

The planning phase involved not only the selection of targets and the timing of the attack but also careful consideration of the challenges posed by the harbor’s defenses, including anti-submarine nets and patrolling naval vessels.

The Attack on Sydney Harbor

The attack was carried out by a group of midget submarines, part of the Japanese Navy’s Special Attack Units. These small, stealthy vessels were designed for infiltration and attack missions in enemy waters. On the eve of the attack, the mother submarines, which had transported the midget submarines close to Sydney Harbor, released them into the sea.

The plan was for these midget submarines to navigate their way into the harbor undetected, bypassing the harbor defenses, and launch torpedoes at the Allied naval vessels anchored there.

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The midget submarines faced significant challenges from the outset. Sydney Harbor’s defenses included anti-submarine nets, patrol boats, and searchlight-equipped defense stations.

The first submarine, M-14, attempted to enter the harbor but became entangled in the anti-submarine netting that protected the harbor entrance. Despite desperate efforts to free itself, the submarine was detected and attacked, ultimately leading its crew to self-destruct the vessel to avoid capture.

The other two submarines, M-21 and M-24, managed to navigate through the harbor’s defenses. M-21 launched a torpedo at the USS Chicago, a heavy cruiser and the primary target of the attack. However the torpedo missed its intended target and instead struck the HMAS Kuttabul, a barracks ship, causing significant casualties.

HMAS Kuttabul was a Sydney Ferry before the war. Seen here in 1922.

The presence of the midget submarines prompted an immediate and chaotic response from the harbor’s defenses. The attack threw the harbor into a state of high alert, with naval vessels scrambling to avoid torpedoes and counter the submarine threat. The response included depth charge attacks and intense searching by naval and air units to locate and neutralize the remaining submarines.

The fate of the midget submarines reflects the high risks associated with their mission. M-21, after launching its attack, was detected and subjected to depth charge attacks. Its crew ultimately scuttled the submarine, choosing to die rather than be captured.

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M-24, the only submarine to successfully fire on and miss its primary target without being immediately detected, disappeared after the attack, leading to a long-standing mystery regarding its fate. It was much later discovered off Sydney’s northern beaches, its crew having also chosen a warrior’s death.

The immediate military outcomes of the attack were relatively limited. The physical damage inflicted was not as significant as might have been expected from such a daring operation. However, the sinking of the HMAS Kuttabul, with the loss of 21 sailors, was a tragic outcome, underscoring the human cost of the attack.


The attack had significant military and strategic consequences for both the Allies and Japan. For the Allies, particularly Australia, the raid exposed vulnerabilities in coastal defenses and highlighted the need for enhanced vigilance and preparedness against potential Japanese incursions.

In response, Australia and its allies fortified their coastal defenses, expanding anti-submarine nets, improving surveillance and intelligence operations, and increasing the readiness of naval and air forces in and around strategic ports.

Submarine 14 was raised from the seabed the day after the attack.

This event also prompted a reassessment of Allied naval strategies in the Pacific, emphasizing the need for a more aggressive and forward-leaning posture to counter the Japanese threat. It catalyzed a shift towards offensive operations, aiming to take the fight closer to Japanese-held territories, thereby reducing the risk of similar attacks on Allied bases.

The psychological impact of the attack was profound and widespread. For the Australian public, the raid shattered any lingering illusions of immunity from the global conflict. The realization that the war had reached their shores, capable of inflicting loss of life and damage within a major city’s heart, was a sobering moment. It galvanized the Australian populace, fostering a stronger resolve and unity against the Axis powers, and bolstering recruitment and support for the war effort.

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Internationally, the attack demonstrated the global reach of the Japanese military and its willingness to undertake bold and innovative operations. This served as a warning to Allied nations, underlining the necessity of a cohesive and determined effort to counteract the Japanese expansion and aggression in the Pacific.

For Japan, the attack on Sydney Harbor, despite its limited tactical success, was initially touted as a demonstration of Japanese naval prowess and the ability to strike deep into enemy territory. However, the long-term strategic benefits were negligible.

The raid did not significantly alter the balance of power in the Pacific or diminish the Allies’ resolve. Instead, it contributed to the eventual escalation of Allied military activities in the Pacific theater, which would, over time, put Japan on the defensive.

The raid left a lasting legacy, remembered through memorials, historical studies, and public commemorations that honor those who lost their lives in the attack and the subsequent defense efforts.