The Japanese midget submarine attack on Sydney Harbour was audacious and would have been even more spectacular had the primary military targets been successfully damaged. The attack showed the vulnerability of ports like Sydney, Australia, to long-range Japanese submarine patrols and the need for heightened security. Many Sydney-siders still recall the moments at night on 31 May / 1 June 1942 as the harbour lit up with depth charge explosions, tracer fire and criss-crossing harbour defence vessels.  The explosion as a Japanese torpedo struck under the depot ferry HMAS Kuttabul was intense, throwing portions of the shattered hull high into the sky and killing twenty-one men.
 
The attack mirrored the earlier midget submarine operations at Pearl Harbour  (7 December 1941) and the raid on Diego Suarez in Madagascar (30 May 1942).  The Sydney raid involved five large ocean going submarines, I-22, I-24, I-27 with their three midget submarines, and I-21 and I-29 providing support.  A sixth intended submarine I-28 was sunk by the US submarine USS Tautog before it could deploy with a fourth midget. The five remaining mother-submarines, which had left Truk (Chuuk) Lagoon in the Pacific, arranged themselves in a semi-circle centred on Sydney Heads.  A previous flight (29 May) by a reconnaissance aircraft launched from I-21 has spotted potential targets inside the harbour.  This Glen-type twin-float seaplane capsized when returning to its submarine and was scuttled.  The remains have not been located.

At about 8pm on the Sunday evening, the first midget (number Ha-14 from I-27) commanded by Sub Lieutenant Lieutenant Chuman, motored submerged into the harbour.  Unfortunately for its crew, the boat became fouled inside the still incomplete anti-submarine boom net laid across the harbour between Georges Head and Green Point near Watson's Bay.  Observed by surface craft near the Western Gate, the two-man Japanese crew decided to commit suicide when escape was hopeless.  They fired the forward internal scuttling charge about 10.30pm and destroyed the fore end of the submarine.  Remains of the wreck and its crew were later recovered.

Midget A (according to the Allied order of identification) from I-24 (or M24), commanded by Sub Lieutenant Ban with Petty Officer Ashibe, next entered the harbour and followed a Manly ferry through the boom defences.  The exact serial number of this submarine has not been ascertained. The submarine crossed the Indicator Loop system at about 9:48 pm.  In a cat-and-mouse play, the submarine manoeuvred around the harbour and was sighted several times around 11:00 pm.  Under fire from the heavy Cruiser USS Chicago and several other vessels, the submarine successfully fired its two torpedoes about 12.30am from near Bradleys Head.  Both missed Chicago - the prime target, one running onto Garden Island and failing to explode.  The other struck under the ferry HMAS Kuttabul after passing under the Dutch submarine K-IX at its berth.  The explosion sank Kuttabul and killed 21 of those aboard.  Ban's midget submarine was never recovered.  Many theories were advanced for its probably resting-place, with wartime confirmation that the crew never made it back to the planned rendezvous point immediately south of Port Hacking.

The third midget, Ha-21 from I-22 commanded by Lieutenant Matsuo crept into the harbour and was sighted near the Heads about 11.00pm, was depth charged, laid low for several hours, and made a belated entry around 3:00am when Chicago was leaving port. The boat was variously sighted in the vicinity of Bradleys Head and Taronga Zoo until detected in Taylors Bay by 5:00 am.  The midget was attacked with depth charges from HMAS Seamist, Steady Hour and Yarroma until 8:30 am in the morning of 1 June and fatally crippled.  When recovered with its two live torpedoes and unexploded (though fired) scuttling charges, the crew were found dead, having committed suicide using Matsuo's service pistol. The remains of Ha-14 and Ha-21 were recovered from the harbour within a week and subjected to military interrogation.

The Type A Japanese midget submarines used in the Sydney raid were approximately 24 metres (80 feet) in length, had a crew of two, carried two 18-inch torpedoes, had pre-charged batteries driving a 600hp electric motor, and could remain submerged for about 12 hours. On display at the Australian War Memorial, Canberra, is a composite craft made up of the remains of midget Ha-14 and Ha-21, while the remaining conning tower (from Ha-21) is on display at the Naval Heritage Centre, Garden Island, Sydney. None of the five mother submarines survived wartime operations.  Interestingly, I-22 and I-24 had launched previous midget submarines during the Pearl Harbour attack of 1941 six months before. 

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