The 'Raid on Sydney Harbour' was a Japanese midget submarine attack on Allied warships in the harbour of Sydney, the main city and port of New South Wales in eastern Australia, and also on Newcastle to the north-north-east of Sydney (31 May/8 June 1942).

On the night of 31 May/1 June, three two-man 'Type A' class midget submarines (M-14, M-21 and M-24 entered Sydney harbour, avoided the partially completed harbour anti-submarine boom net and sought to sink Allied warships. Two of the midget submarines were detected and attacked before they could engage any Allied vessels: the crew of M-14 scuttled their boat, and M-21 was attacked and sunk, its crew killing themselves. These boats were later recovered by the Allies. The third submarine attempted to torpedo the US heavy cruiser Chicago, but instead sank the Australian converted ferry Kuttabul, killing 21 sailors. This boat’s fate remained unknown until 2006, when amateur divers discovered the wreck off Sydney’s northern beaches.

Immediately after the raid, the five Japanese fleet submarines which had carried the midget boats to Australia embarked on a campaign to disrupt merchant shipping in eastern Australian waters. Over the next month, the submarines attacked at least seven merchant vessels, sinking three of them and killing 50 sailors. During this period, between 00.00 and 02.30 on 8 June, two of the submarines bombarded the ports of Sydney and Newcastle.

The midget submarine attacks and subsequent bombardments are among the best-known examples of Axis naval activity in Australian waters during World War II, and are the only occasion in history when either city has come under attack. The physical effects were slight: the Japanese had intended to destroy several major warships, but sank only an unarmed depot ship and failed to damage any significant targets during the bombardments. However, the main impact was psychological inasmuch as it created a popular fear of impending Japanese invasion and forced the Australian military to upgrade the defences, the latter including the introduction of convoy operations to protect merchant shipping.

The Imperial Japanese navy originally intended to use six cruiser submarines as the basis for the attack on Sydney harbour: these were the 'Type B1' class I-21, I-27, I-28 and I-29, and the 'Type C1' class-I-22 and I-24. These six boats constituted the Eastern Attack Group of the 8^th Submarine Squadron under the command of Captain Hankyu Sasaki. 

On 8 June 1942, I-21 and I-29, each carrying one Yokosuka E14Y1 'Glen' single-engined reconnaissance floatplane scouted various Australasian harbours to select those most vulnerable to attack by midget submarines. I-21 scouted Nouméa in New Caledonia island, Suva in the Fijian islands group and Auckland in New Zaland, while I-29 surveyed Sydney.  On 11 May, the other four boats (I-22, I-24, I-27 and I-28) were ordered to the Japanese naval base at Truk lagoon in the Caroline islands group, where each was to be loaded on its after decking with a 'Type A' class midget submarine. I-28 failed to reach Truk as it was torpedoed on the surface by the US submarine Tautog on 17 May.  The three remaining submarines left Truk on about 20 May for a point to the south of the Solomon islands group. I-24 was forced to return one day later, however, after an explosion in her midget submarine’s battery compartment killed the boat’s navigator and injured its commander, and the midget submarine which had been intended for I-28 replaced the damaged boat.

The naval officer in charge of Sydney barbour at the time of the attack was a Briish officer, Rear Admiral G. C. Muirhead-Gould. On the night of the attack, three major Allied warships were present in Sydney harbour: these were the heavy cruisers Chicago and Australian Canberra, and the Australian light cruiser Adelaide. Other warships in the harbour included the US destroyer tender Dobbin, the Australian auxiliary minelayer Bungaree, the Australian corvettes Whyalla and Geelong, the Indian corvette Bombay, the armed merchant cruisers Kanimbla (British) and Westralia (Australian), and the Free Dutch submarine K-IX. An Australian converted ferry, Kuttabul, was alongside at Garden Island to serve as a temporary barracks for sailors transferring between ships.  The Free Dutch hospital ship Oranje had also been in the harbour, but departed an hour before the attack.

At the time of the attack, Sydney harbour’s static defences consisted of eight anti-submarine indicator loops (six outside the harbour, one between North Head and South Head, and one between South Head and Middle Head) as well as the partially completed Sydney harbour anti-submarine boom net between George’s Head on Middle Head and Laing Point (formerly known as Green Point) on Inner South Head.  The central section of the net had been completed, and support piles were in place to the west, but 1,300-ft (395-m) gaps remained on each side as material shortages had prevented the completion of the boom net. On the day of the attack, the six outer indicator loops were inactive: two were not functioning and there were not enough trained personnel to man both the inner and outer loop monitoring stations.  The North Head/South Head indicator loop had been giving faulty signals since a time early in 1940, and as civilian traffic regularly passed over the loop, the readings were often ignored.

The Australian harbour defence craft included the anti-submarine vessels Yandra and Bingera, the auxiliary minesweepers Goonambee and Samuel Benbow, the pleasure launches Yarroma, Lolita, Steady Hour, Sea Mist, Marlean and Toomaree converted to channel patrol boats with depth charge armament, and four unarmed naval auxiliary patrol boats.

The Imperial Japanese navy had used five 'Type A' class midget submarines in an unsuccessful operation against US battleships during the 'Ai' attack on Pearl Harbor in December 1941, and now hoped that upgrades to the submarines, intensified crew training and the selection of a less well defended target would provide better results and an increased chance for the crews of the midget boats to return alive from their mission. On 16 December 1941, therefore, the Imperial Japanese navy began planning a second midget submarine operation.

The resulting plan called for a pair of simultaneous attacks against Allied naval vessels in the Indian Ocean and South Pacific Ocean. These attacks were intended as diversions ahead of the 'Mi' (ii) attack on Midway island in the North Pacific Ocean, the Japanese hoping to convince the Allies that they intended to attack to the south or west of their current conquests. Some 11 submarines of the 8^th Submarine Squadron were to carry out the two attacks, the five submarines of the Western Attack Group in the Indian Ocean, and the six submarines of the Eastern Attack Group in the Pacific Ocean. Based on its own reconnaissance, each group was to select a port suitable for attack.

The Western Attack Group selected Diégo Suarez at the northern tip of the island of Madagascar. This attack, which took place at the fall of night on 30 May, resulted in the damaging of the British battleship Ramillies and the sinking of the tanker British Loyalty, was delivered 22 days after the British captured the port from Vichy France at the beginning of the 'Ironclad' operation to take Madagascar.

The four potential targets for the Eastern Attack Group were Nouméa, Suva, Auckland and Sydney.  Identified by reconnaissance flights flown by Warrant Flying Officer Nobuo Fujita operating from I-25: from 17 February the Japanese floatplane flew over Sydney harbour, and the eastern Australian harbours of Melbourne and Hobart (1 March), followed by the New Zealand harbours of Wellington (8 March) and Auckland (13 March). I-21 and I-29 were sent to select the final target, with I-29 sailing to Sydney.  On the evening of 16 May, I-29 fired on the 5,135-ton Soviet merchant vessel Wellen in a location some 30 miles (48 km) from Newcastle in New South Wales: although Wellen escaped with minimal damage, shipping between Sydney and Newcastle was halted for 24 hours while aircraft and all available anti-submarine ships from Sydney, including the Free Dutch light cruiser Tromp, Australian destroyer Arunta and US destroyer Perkins, searched unsuccessfully for the submarine.  Muirhead-Gould then came to the conclusion that the submarine had operated alone and had left the area immediately after the attack.

I-29's floatplane made a reconnaissance flight over Sydney on 23 May.  A secret radar unit set up in Iron Cove detected the flight, but the authorities dismissed its report as a glitch as there were no Allied aircraft operating over Sydney. The floatplane was damaged or destroyed on landing, although its two-man crew survived and reported the presence of several capital ships, including two battleships or large cruisers, five other large warships, several minor war vessels and patrol boats, and prolific merchant shipping.  The report, which the Allied FRUMEL (Fleet Radio Unit, Melbourne) signals intelligence network partially intercepted, led the Imperial Japanese navy to select Sydney as the target. The three midget-carrying submarines rendezvoused with I-29 and I-21 about 35 miles (56 km) to the north-east of Sydney Heads, where all five submarines were in position by 29 May.

Before dawn on 29 May, I-21's floatplane, flown by Ito Susumu, undertook a final reconnaissance flight over Sydney harbour with the task of mapping the locations of the major vessels and of the anti-submarine net. Many people on the ground spotted the floatplane but assumed it was a Curtiss SOC Seagull floatplane of the US Navy despite the fact that the Japanese aeroplane was a monoplane rather than a biplane and had a side-by-side pair of main floats whereas the US machine had a single main float.  Therefore no alarm was raised until 05.07, after it had been realised that the only ship in the area carrying the Seagull was the US cruiser Chicago, which had all for of its floatplanes on board. Richmond air force base launched CAC Wirraway single-engined fighters, which failed to locate either I-21 or the floatplane. Thus he Japanese reconnaissance flight did not result in the authorities in Sydney taking any special defence measures. The floatplane was seriously damaged on landing and had to be scuttled, but both men of its crew survived.

The Japanese planned to launch the midget submarines one after the other between 17.20 and 17.40, from points 5.8 to 8.1 miles (9.3 to 13 km) outside Sydney harbour. The first midget was to pass through the Heads just after 18.30, but heavy seas delayed it by more than one hour.  The other two midgets followed at 20-minute intervals and were similarly delayed. The choice of targets was left up to the midget submarine commanders, with advice that they should primarily target aircraft carriers or battleships, with cruisers as secondary targets. The midgets were to operate to the east of the Harbour Bridge, although if no suitable targets were to be found in this area they were to move under the bridge and attack a battleship and large cruiser believed to be in the inner harbour. When the second reconnaissance overflight revealed that the expected British battleship Warspite was not present, the cruiser Chicago became the priority target.

After completing their mission, the midgets were to depart Sydney harbour and head 23 miles (37 km) to the south to the recovery point off Port Hacking.  Four of the mother submarines would be waiting in an east/west line 9.9 miles (16 km) long, with the fifth waiting 3.7 miles (6 km) farther to the south.

Launched from I-27, M-14 was the first to enter Sydney harbour.  The Middle Head/South Head loop detected the boat at 20.01, but dismissed the reading as a result of heavy civilian traffic.  At 20.15, a watchman of the Maritime Services Board spotted the midget after it passed through the western gap, collided with the Pile Light, then reversed and trapped its stern in the net.  The submarine’s bow broke the surface. The watchman rowed toward it to determine what it was and then rowed to the nearby patrol boat Yarroma to report his finding.  Despite Yarroma's efforts to pass on this information, Sydney Naval Headquarters did not receive the report until 21.52, and then despatched Yarroma and Lolita to investigate. On confirming that the object in the net was a 'baby submarine', Lolita dropped two depth charges while Yarroma's commander requested permission from Sydney Naval Headquarters to open fire.  The depth charges failed to detonate as the water was too shallow for the hydrostatic fuse setting.  At 22:35, as Yarroma awaited permission to fire and Lolita was preparing to deploy a third depth charge, the M-14's two crewmen activated one of the submarine’s scuttling charges, killing themselves and destroying the submarine’s forward section.

Muirhead-Gould gave the general alarm, along with orders for ships to take anti-submarine measures, at 22.27. The alarm was repeated at 22.36 with advice for ships to take precautions against attack, as an enemy submarine might be in the harbour.  At the time of the first alarm, Sydney harbour was closed to external traffic, but Muirhead-Gould ordered ferries and other internal traffic to continue, as he believed that having multiple ships travelling around at speed would help force any submarines to remain submerged. 

M-24 was the second boat to enter the harbour. The Royal Australian Navy’s ketch Falie, an examination vessel, grazed M-24's hull and reported the contact to command, but the report triggered no further action. M-24 crossed the indicator loop undetected at 21.48, and at about 22.00 followed a Manly ferry through the anti-submarine net.  At 22.52, M-24 was spotted by a Chicago searchlight operator less than 1,600 ft (490 m) off the moored cruiser’s starboard side, and on a course roughly parallel to the ship’s facing. Chicago opened fire with a 5-in (127-mm) gun and a quadruple machine gun mount, but inflicted minimal damage as the weapons could not depress far enough. Some of the 5-in (127-mm) shells skipped off the water and hit the Fort Denison park’s Martello tower, while fragments were later found in the suburbs of Cremorne and Mosman.  The senior officer present aboard Chicago preparations for sea and for Perkins to begin an anti-submarine screening patrol around the cruiser, but these orders that were revoked by the sceptical Captain Howard Bode when he arrived on board at about 23.30.

Whyalla and Geelong also fired on M-24 as it fled to the west in the direction of the Sydney Harbour Bridge, before the midget was able to submerge and escape.  When it returned to periscope depth, the midget found itself to the west of Fort Denison, turned and headed to the east for about 1.2 miles (1.9 km), then took up a firing position to the south-west of Bradley’s Head, from where its commander could see Chicago's stern silhouetted against the construction floodlights at Garden Island’s new Captain Cook Graving Dock.

Launched from I-22, M-21 probably entered the harbour at the same time that Chicago opened fire on M-24.  The unarmed naval auxiliary patrol boat Lauriana spotted M-21 and illuminated the little submarine’s conning tower, while sending an alert signal to the Port War Signal Station at South Head, and the nearby anti-submarine vessel Yandra. The latter attempted to ram the submarine, lost contact, regained contact at 23.03, and fired a full pattern of six depth charges. At the time of the attack, it was assumed that the depth charges had destroyed or disabled the midget, but M-21 survived. It is believed that the midget took refuge on the harbour bottom and waited until the Allied vessels had moved away before resuming its attack.

At 23.14, Muirhead-Gould ordered all ships to observe black-out conditions and, just after 23.30, set off on a barge toward the boom net in order to make a personal inspection. The admiral reached Lolita at about 00.00 and indicated to her crew that he did not take the reports of enemy submarines seriously, reportedly saying 'What are you all playing at, running up and down the harbour dropping depth charges and talking about enemy subs in the harbour? There’s not one to be seen.' The crew reiterated that a submarine had been seen, but Muirhead-Gould remained unconvinced and, before he left, added sarcastically that 'If you see another sub, see if the captain has a black beard. I’d like to meet him.'

Despite the black-out order, the Garden Island floodlights remained illuminated until 00.25. About five minutes later, M-24 fired the first of its two 450-mm (17.72-in) torpedoes, but delayed firing the second torpedo for several minutes as the midget submarines lost longitudinal stability immediately after firing a torpedo. There is uncertainty about the exact paths of the torpedoes relative to Chicago, though there is general agreement that the US cruiser was the intended target. Both torpedoes missed Chicago, while one torpedo may have also passed close to Perkins's starboard bow. One of the torpedoes continued underneath the Free Dutch submarine K-IX and the Australian Kuttabul, then hit the breakwater to which Kuttabul was moored. The explosion broke Kuttabul in two and sank her, and damaged K-IX. The attack killed 19 Australian and two British sailors, and wounded another 10. The explosion shook houses in the area and damaged Garden Island’s lights and telecommunications. The other torpedo ran aground on the eastern shore of Garden Island without exploding. M-24 then dived and moved to leave the harbour.

A crossing over the indicator loop recorded at 01.58 was initially believed to be another midget submarine entering the harbour, although later analysis showed that the reading indicated an outbound vessel and therefore most likely represented M-24's exit. The boat did not return to its mother submarine, and its fate remained unknown until 2006.

Ships were ordered to make for the open ocean. Chicago left her anchorage at 02.14, leaving a sailor behind on the mooring buoy in her haste to depart. Bombay, Whyalla, Canberra and Perkins began their preparations to depart.

Just before 03.00, as Chicago was leaving the harbour, look-outs spotted a submarine periscope passing alongside the cruiser. At 03.01, the indicator loop registered an inbound signal as M-21 re-entered Sydney harbour after recovering from the attack four hours earlier. Kanimbla fired on M-21 in Neutral Bay at 03.50, and at 05.00 the auxiliary patrol boats Steady Hour, Sea Mist and Yarroma spotted the submarine’s conning tower in Taylors Bay. The patrol boats had set their depth charge fuses to 15 m (49 ft), and when Sea Mist passed over the pint at which the submarine had just submerged and dropped a depth charge, she had only five seconds to clear the area. The resulting blast damaged M-21, which inverted and rose to the surface before sinking again. Sea Mist dropped a second depth charge, which damaged one of her two engines in the process and prevented her from making further attacks.  Steady Hour and Yarroma continued the attack, dropping 17 depth charges on believed visual sightings and instrument contacts of the midget over the next three and a half hours. At some point during the night, the crew of M-21 killed themselves. 

At 04.40, Canberra recorded that the Japanese might have fired torpedoes at her. This may have been one of many false alarms throughout the night. However, M-21 had attempted to fire its two torpedoes, but failed because of damage to the bow either from Yandra's ramming or depth charges, or a possible collision with Chicago, making it possible that M-21 did make an attempt to attack the Australian cruiser. The observer aboard Canberra may have seen bubbles from the compressed air released to fire the torpedoes.

In accordance with operation’s plan, the five mother submarines waited off Port Hacking on the nights of 1 and 2 June for the midget submarines to return. FRUMEL picked up wireless traffic between the five submarines, leading the Royal Australian Air Force to task three Lockheed Hudson twin-engined coastal reconnaissance/bombers and two Bristol Beaufort twin-engined maritime attack bombers with finding the source of the communications, but the aircraft were unsuccessful. On 3 June, Sasaki abandoned hope of recovering the midget submarines, and the submarines dispersed on their secondary missions. 

Four of the submarines began operations against Allied merchant shipping. I-21 patrolled to the north of Sydney and I-24 to the south of it. I-27 began searching off Gabo island for ships departing Melbourne, and I-29 travelled to the waters off Brisbane. I-22 left the group to conduct reconnaissance operations, first at Wellington and Auckland in New Zealand, and then at Suva in the Fijian islands group.

Between 1 and 25 June, when the four submarines arrived at Kwajalein atoll in the Marshall islands group for resupply before proceeding to Japanese shipyards for maintenance, the four submarines attacked at least seven Allied merchant vessels.  Three of these were sunk: Iron Chieftain by I-24 on 3 June, Iron Crown by I-27 on 4 June and Guatemala by I-21 on 12 June. The first two of these attacks resulted in 12 and 37 fatalities respectively, but the third attack killed no one. The attacks forced the authorities to institute changes in merchant traffic, and travel to the north of Melbourne was restricted until a system of escorted convoys had been established.

I-21 was the only submarine to return to Australian waters, where she sank three ships and damaged two others during January and February 1943. During her two deployments to Australian waters, I-21 sank 44,000 tons of Allied shipping, which made her the most successful Japanese submarine to operate in Australian waters.

On the morning of 8 June, I-24 and I-21 briefly bombarded Sydney and Newcastle. Just after 00.00, I-24 surfaced 9 miles (14 km) to the south-south-east of Macquarie Lighthouse, and the submarine’s commander ordered the gun crew to target the Sydney Harbour Bridge. The 140-mm (5.51-in) deck gun fired 10 shells over a four-minute period, and of these nine landed in the city’s eastern suburbs and one landed in the water. I-24 then crash-dived to prevent successful retaliation by coastal artillery batteries. Only one of the boat’s shells detonated, and the only injuries inflicted were cuts and fractures from falling bricks or broken glass when the unexploded shells hit buildings. A USAAF pilot, 1^st Lieutenant George Cantello, based at Bankstown Airport, disobeyed orders and took off in an effort to locate the source of the shelling, but was killed when engine failure caused his Bell P-39 Airacobra single-engined fighter to crash in a paddock at Hammondville.

At 02.15, I-21 shelled Newcastle from a range of 5.6 miles (9 km) to the north-east of Stockton Beach.  The boat fired 34 150-mm (5.91-in) shells, including eight star shells, over a 16-minute period. The attack’s target was the BHP steelworks, but the shells landed over a large area, causing minimal damage and no fatalities: the only shell to detonate damaged a house on Parnell Place, while an unexploded shell hit a tram terminus. Fort Scratchley returned fire, the only time an Australian land fortification has fired on an enemy warship during wartime, but the submarine escaped unscathed.

The attack on Sydney Harbour ended in failure on both sides, and revealed flaws in both the Allied defences and the Japanese tactics. During the primary attack, the Japanese lost all three midget submarines in exchange for the sinking of a single barracks ship. The subsequent operations were no more successful as the five large Japanese submarines sank only three merchant ships and caused minimal property damage during the two bombardments. The performance of the Allied defenders was equally poor.

The main impact of the midget submarine attack and subsequent operations was psychological, for it dispelled any belief that Sydney was immune to Japanese attack and highlighted Australia’s proximity to the Pacific War.  There was no official inquiry into the attacks, despite demand from some sections of the media, as there was concern that an inquiry would lead to defeatism and reduce faith in John Curtin’s government, particularly after the damaging inquiry into Australian defences that had followed the Japanese aerial attack on Darwin three months earlier.

The Allies failed to respond adequately to several warnings of Japanese activity off Australia’s eastern coast before the attack, simply ignoring the warnings or explaining them away. They attributed the unsuccessful attack on the freighter Wellen on 16 May to a single submarine which, they assumed, had departed Australian waters immediately after the attack.  The first reconnaissance flight went unnoticed, and although FRUMEL intercepted the report and distributed it to Allied commanders on 30 May, Muirhead-Gould apparently did not react. New Zealand naval authorities detected radio chatter between the Japanese submarines on 26 and 29 May, and although they could not decrypt the transmissions, radio direction finding indicated that a submarine or submarines were approaching Sydney.  The Allies considered the despatch of an anti-submarine patrol in response to the 29 May fix, but were unable to do so as all anti-submarine craft were already committed to protecting a northbound troop convoy.  The only response to the second reconnaissance flight on 29 May was the launching of search aircraft. No other defence measures were put into place.  Although the midget submarine attack on Diégo Suarez in Madagascar occurred on the morning of 31 May, the Allies sent no alert to other command regions as they believed that Vichy French forces had launched the attack.

During the attack, there were several delays between events and responses to them. More than two hours passed between the observation of M-14 in the boom net and Muirhead-Gould’s first order for ships to begin anti-submarine actions, and it took another two hours to mobilise the auxiliary patrol boats, which did not leave their anchorage for a further hour. Part of these delays was the result of ineffective communications: none of the auxiliary patrol craft in the harbour had radio communications, so all instructions and reports came from signal lights via the Port War Signal Station or Garden Island, or by physical communication via launches.  In his preliminary report on the attack, Muirhead-Gould stated that the Port War Signal Station was not designed for the volume of communications traffic the attack caused. Telephone communications with Garden Island were unreliable during the early part of the attack, and then the first torpedo explosion disabled them completely.

The need to keep information secret may also have contributed to the delays and the defenders' scepticism. As the auxiliary patrol boat crews, the indicator loop staff, and other personnel manning defensive positions were outside 'need to know' and had not been informed about any of the incidents before the attack and were not on alert, contributing to the disbelief demonstrated in the early hours of the attack.

The main flaw in the Japanese plans was the use of midget submarines for the primary attack. Midget submarines were originally intended to operate during fleet actions: they would be released from modified seaplane carriers to run amok through the enemy fleet.  This concept went out of favour as changing Japanese naval thinking and experience led to recognition that naval warfare would centre around carrierborne air combat.  As a result, the midget submarine programme’s focus changed to the infiltration of enemy harbours, where they would attack vessels at anchor.  This concept failed completely during the attack on Pearl Harbor, where the midget submarines had no effect, and tying up 11 large submarines for six weeks in support of further midget submarine attacks on Sydney and Diégo Suarez proved a waste of resources.

Moreover, the failures at Sydney Harbour and Diégo Suarez demonstrated that the improvements to the midget submarines implemented after Pearl Harbor had not increased the overall impact of the midget submarine programme. The modifications had various effects. The ability to man and deploy the midgets while the mother ships were submerged prevented coastal radars from detecting the mother submarines, but the midget submarines were still difficult to control, unstable and prone to porpoising (surfacing or diving uncontrollably).