During March 1944, the Allies of World War II rapidly reinforced the military units located in the state of Western Australia to defend against the possibility that Japanese warships would attack the cities of Fremantle and Perth. This redeployment began on 8 March after concerns were raised about the purpose of Japanese warship movements near the Dutch East Indies, and ended on 20 March, after it was concluded that an attack was unlikely.
In February 1944, the Allies became alarmed that the movement of the main Japanese fleet to Singapore could be a precursor to raids in the Indian Ocean, including against Western Australia. The emergency began when Allied code breakers detected the movement of a powerful force of Japanese warships in the Netherlands East Indies in early March. After a United States Navy submarine made radar contact with two Japanese warships near one of the entrances to the Indian Ocean on 6 March, the Allied military authorities and Australian Government judged that a fleet may have been heading towards the Perth area. In reality, these warships were undertaking a patrol while awaiting a small raiding force to return from attacking ships in the central Indian Ocean.
In response to the perceived threat, the Allied military units stationed in Western Australia were placed on alert, and reinforcements were dispatched. These included six Royal Australian Air Force flying squadrons. Other Allied air units were held at Darwin in the Northern Territory to respond to raids on that town or reinforce Western Australia if the Japanese fleet was sighted. An air raid warning was sounded in Fremantle and Perth on 10 March, but this proved to be a false alarm. Intensive patrols by the Allied militaries did not detect any Japanese warships off Western Australia, and most units stood down on 12 March. On 20 March, it was concluded that the threat of attack had passed, and the air reinforcements that had been sent to Western Australia returned to their bases.
Background
Allied defences Fremantle, Western Australia was an important port throughout World War II. From the start of the war, it was the assembly point for convoys of Allied ships travelling between Australia, the Middle East, and Europe. Soon after the outbreak of the Pacific War, the city became a key operating and maintenance location for United States Navy submarines. The Fremantle submarine base was established in March 1942, and eventually became the US Navy's second-largest submarine base, after Pearl Harbor in Hawaii. Royal Netherlands Navy submarines were also stationed at Fremantle from 1942, and the Royal Navy began transferring submarines there in mid-1944. Allied submarines operating from Fremantle played a key role in the offensive against Japanese shipping; over the course of the war, 154 submarines made 341 combat patrols from the port.
The Australian Government and local civilians regarded the geographically isolated Perth–Fremantle area as being vulnerable to attack. These fears peaked in March 1942 following the rapid Japanese advance through South East Asia during December 1941 and the early months of 1942. No Japanese attack on the region eventuated, though several small towns in the north of Western Australia were bombed. Concerns over Fremantle's security continued; in March 1943 Australian Prime Minister John Curtin noted as part of a message to British Prime Minister Winston Churchill and US President Franklin D. Roosevelt that the port was vulnerable to bombardment by Japanese warships or aircraft flying from aircraft carriers.
Elements of the Australian and United States armed forces were assigned to the defence of the Perth–Fremantle area. Each of Australia's three armed services maintained a separate headquarters in Western Australia, their efforts coordinated by Combined Defence Headquarters. In the event of attack, the Australian Army's III Corps would assume overall control. By early 1944, the forces assigned to the region's defence had been reduced from their peak strength. Nevertheless, several anti-aircraft and coastal defence batteries were located in and near Perth and Fremantle to protect the cities from attack. These units were primarily manned by Volunteer Defence Corps (VDC) part-time personnel, who would be called up if a threat developed. Three Royal Australian Air Force (RAAF) flying squadrons were also stationed around Perth; No. 85 Squadron provided air defence with CAC Boomerang fighters, No. 14 Squadron patrolled off the Western Australian coast using Bristol Beaufort light bombers and No. 25 Squadron operated Vultee Vengeance dive bombers. The US Navy's Patrol Wing 10 augmented the Australian forces and conducted long-range patrols over the Indian Ocean from Perth with Consolidated PBY Catalina flying boats.
Japanese redeployments In February 1944, the Combined Fleet, the Imperial Japanese Navy's main striking force, withdrew from its base at Truk in the Central Pacific to Palau and Singapore. The appearance of a powerful naval force at Singapore alarmed the Allies, as it was feared that these ships would conduct raids into the Indian Ocean and against Western Australia. In response, the Allies strengthened the British Eastern Fleet in the central Indian Ocean by transferring two British light cruisers from the Atlantic and Mediterranean as well as several US Navy warships from the Pacific. The number of air units in Ceylon and the Bay of Bengal region was also increased. Reinforcements for the 16 US Navy submarines based at Fremantle were also dispatched, but most of these boats did not arrive until after mid-March. The submarines were tasked with attacking the Japanese fleet in South East Asian waters.
General Douglas MacArthur's General Headquarters, which was responsible for the South West Pacific Area, assessed in February that the Combined Fleet could potentially attack the port of Fremantle. It was thought that the purpose of any such raid would be to divert Allied forces from the offensives they were about to launch in the Pacific. MacArthur did not move any additional forces to Western Australia at this time, but developed plans to reinforce the area if necessary. Land-based aircraft were considered sufficient to counter any attacks on Fremantle and, on 28 February, General Headquarters directed Lieutenant General George Kenney, the commander of the Allied Air Forces, to prepare to:
Concentrate a striking force of sixty heavy bombers in Western Australia on twenty-four hours' notice. Reinforce this heavy bomber striking force with medium bombers when directed by this headquarters. Provide three fighter squadrons for the defence of Perth. Operate heavy and medium bombers from Darwin, Corunna Downs, Geraldton and Carnarvon Supply the air forces operating in Western Australia by air in an emergency.
On 4 March, Curtin sent a cable to Churchill seeking the British Government's assessment of the likelihood of Japanese raids into the Indian Ocean, and the capacity of the Allied forces in the region to defeat any such attacks. Curtin's cable crossed a message Churchill had sent the previous day, which stated that while Japanese forces could conduct raids against Allied shipping in the Indian Ocean, "it is not thought that serious danger, either to India or to Western Australia, is likely to develop". Churchill's cable also noted that the Japanese would likely seek to preserve their remaining major warships for use in the later stages of the war.
Although the Australian Government was reassured by Britain's assessment of the situation, the Allied military units stationed in Western Australia made preparations to resist a possible attack. The RAAF's Western Area Command improved the readiness of its forces near Perth and Exmouth Gulf in the north-west of the state. It also stockpiled bombs at Cunderdin, north-east of Perth, to be used by any heavy bombers sent as reinforcements. The readiness of the Army garrison units in the Perth–Fremantle area was also increased. The Fremantle Fortress command, which was responsible for defending the port against naval bombardment or air attack, was placed on alert and ordered to station more heavy anti-aircraft guns near the city's docks. On 4 March, VDC units were directed to be able to man their assigned anti-aircraft and coastal-defence positions within 6 hours, rather than the normal warning time of 24 hours.
The emergency Japanese movements Despite the Allied concerns, the Japanese did not intend to send the main body of the Combined Fleet into the Indian Ocean. The ships had been withdrawn from the Central Pacific to avoid a major United States offensive that was expected to be launched against the area. Singapore had been selected as the Fleet's new base as it was close to sources of fuel and had suitable facilities to enable the ships to undertake training and maintenance before counter-attacking the Allies in the Pacific. However, it was decided to send a small force of cruisers into the Indian Ocean to conduct the first raid by Japanese surface ships on the area since early 1942.
In late February 1944, Vice-Admiral Shiro Takasu—the Commander in Chief of Japan's Southwest Area Fleet—ordered the heavy cruisers , , and to raid Allied shipping on the main route between Aden and Fremantle. The three ships departed the Combined Fleet's anchorage in the Lingga Islands near Singapore on 27 February. The light cruisers and and three destroyers (which were designated a "Security and Supply Formation") escorted the raiding force through the Sunda Strait on 1 March. These five ships were to remain at sea for the duration of the raid, and then escort the heavy cruisers back through the Sunda Strait. The Allies were not aware of the raiding force or its departure, but Allied code breakers subsequently detected the sailing from Singapore on 4 March of a force comprising two battleships, an aircraft carrier and multiple destroyers, and determined that the ships were headed east towards Surabaya. Rear-Admiral Ralph W. Christie, the commander of the Allied submarines based at Fremantle, believed that this force could attack the Perth–Fremantle area. In response, he ordered the submarine under the command of Lieutenant Commander Chester Nimitz Jr. to patrol the Lombok Strait and report the movement of any Japanese ships into the Indian Ocean.
On 6 March, Haddo briefly made radar contact with, but did not sight, what Nimitz believed may have been at least two large Japanese warships near the Lombok Strait. Nimitz was unsure whether to report this inconclusive contact, but decided to do so to prevent Fremantle from being subjected to a surprise attack; he later wrote that "'Remember Pearl Harbor' was the message that kept sticking in my mind". The Japanese ships detected by Haddo were Kinu and Ōi heading towards the Sunda Strait.
Nimitz's report caused significant concerns. On 8 March, the Australian Chiefs of Staff Committee advised the Australian Government that there was a possibility that the Japanese task force had entered the Indian Ocean with the goal of attacking the Perth–Fremantle area during the full moon period around 9 March. Accordingly, actions were initiated to improve the area's defences. Also on 8 March, the commander of the Eastern Fleet, Admiral James Somerville, directed all Allied ships travelling in the Indian Ocean between 80 and 100° east to divert to the south or west.
Based on the radar contact on 6 March, the phase of the Moon and assumptions of the Japanese force's speed and likely flying-off positions if it included any aircraft carriers, the Allied militaries judged that any attack on the Perth–Fremantle area was most likely to occur during the early hours of 11 March. It was also possible that such an attack could be conducted any time between the night of 9/10 March and the morning of 14 March.
Allied reinforcements