The forces which attacked Pearl Harbour on 7 December 1941, led by Captain Hankyu Sasaki, included five Imperial Japanese submarine carriers - I-16, I-18, I-20, I-22 and I-24. They were all equipped with midget submarines. The Japanese hoped that with an air attack providing distraction, the midget submarines could sneak into the harbour and sink US warships. It was not to be. All the midget submarines were lost, except for one, which ran aground on the beach.
Despite their apparent failure at Pearl Harbour, the Japanese military hoped that by making modifications and improving crew training, the midget submarines could still play an important role in the war.
Admiral Isoroku Yamamoto, head of the Japanese Combined Fleet, was convinced by his staff to pursue another assault. He did so, on the proviso that the midget crews were to be recovered after any attack. Ports at Fiji, Australia and New Zealand were all potential targets.
In late May, the Japanese made two reconnaissance flights over Sydney. The flights were made by specially built small Yokosuka (Glen) seaplanes, with collapsible wings that were carried in components on the ‘I class’ submarines and then reassembled.
The first flight was made on 23 May by Warrant Officer Nobuo Fujita and Petty Officer Second Class Shoji Okuda. The plane did a thorough circuit of the eastern suburbs of Sydney, and the harbour, and reported on naval craft in the harbour. Although the plane was spotted it was ignored because it was thought to be an allied aircraft. It was also detected by a mobile radar unit, located near Iron Cove, but discounted as an aberration on the military’s new experimental radar device.
In the early hours of 29 May, another reconnaissance was undertaken by Flying Warrant Officer Susumu Ito, and his observer, Iwasaki.
In 2002, the then eighty-eight-year-old former Japanese navy pilot, Susumu Ito, who flew the reconnaissance mission over Sydney on the eve of the attack, recounted the experience for Australian filmmaker, Claude Gonzalez (Daily Telegraph, 29 May 2002, p.35)
‘I flew in from North Head, then at South Head I came down to a height of some 500 metres. There appeared to be no lighting restrictions, the whole town was lit up. I even saw a trade ship with its lights on. I was surprised. All seemed so unsuspecting. It was then I started to feel safe, there was little fear I would be attacked.’
On his return to the mother submarine, Ito’s plane hit a wave and flipped over. Ito and his crew member were both thrown a line, and once on deck, watched as their plane was deliberately sunk. The wreck of this aircraft has not been positively identified at this time.
Ito was able to confirm the presence of a large number of naval vessels in Sydney Harbour. This was all that was needed to confirm an assault on Sydney.
The Japanese issued two significant telegraphic orders to their submarine fleet — no. 3 issued on 26 May and no. 4 issued on 29 May. The orders confirmed the nature and date of an attack on Sydney Harbour.
On the evening of 31 May, Captain Hankyu Sasaki, commander of the Eastern Attack Group, which consisted of five 2500 ton I class submarines: I-22, I-24 and I-27 with their midget submarines, and I-21 and I-28, which had been fitted for reconnaissance aircraft, arranged themselves into a semi-circle just outside the heads of Sydney Harbour, between Broken Bay and Port Hacking.
Two of these submarines, I-22 and I-24, had launched midget submarines on Pearl Harbour only six months earlier.
Telegraphic Order No. 3
The following alterations are made re: Sydney Attack —
- Date of the attack will be by a special order (scheduled 31 May).
- Order of dispatching the ‘hangar sheaths’ will be I-27, I-22, then I-24. The time and order for the ‘sheaths’ passing through the heads will be I-27, 20 minutes after moonrise, then I-22 and I-24 following at 20 minute intervals.
- Targets for the attack will be up to the discretion of the ‘sheath’ commanders but try as much as possible to attack the following targets:
- If there is a battleship or large cruiser beyond the Harbour Bridge, then I-22 is to attack the battleship and I-24 the cruiser. If there are two cruisers, then I-22 and I-24 will attack them, and I-27 will attack the battleship.
- If there is a battleship or aircraft carrier outside the Harbour Bridge, then attack it.
- If there are no suitable targets outside of the Harbour Bridge, then try as much as possible to attack the battleship and large cruiser beyond the bridge.
- After the completion of the attack, the following recovery rendezvous is to be taken.
Day 1 … No 4 recovery rendezvous (off Broken Bay)
Day 2 … No 2 recovery rendezvous (off Port Hacking)
Telegraphic Order No. 4
Day of attack … 31 May
The enemy situation in Sydney Harbour is as follows:
- One US battleship 400 metres east of Garden Island. One large US transport ship at 900 metres north of Garden Island. Several destroyers wharved on the west side of Garden Island. (Those have wharfing lights on.) Cockatoo Island has no enemy vessels around it. However, there are two light cruisers and a destroyer inside the dockyard.
- No detection made on the defences of the enemy, but seeing the frequent passage of enemy vessels (in night-time) too) it is presumed that there must be an opening for sea passage. No recognition of enemy patrol boats.
- There are no control lights inside the harbour, the lights at Barrenjoey lighthouse are on.
- There are frequent movements of merchant ships in and out of the harbour and those ships have their lights on. However, there may be false (decoy) wharving lights on.
The following alterations are made to Telegraphic Order no. 3.
- Day one … No. 2 recovery rendezvous (off Port Hacking, south of Sydney). Setting the starting appoints at 180 degrees 4 km off Port Hacking, position at 100 degrees the following vessels: I-29, I-27 and I-24 (in that order). Distance 4km, 190 degrees 6km from the centre position of the retrieval for 1-21.
- For daytime standby (and night-time withdrawal), set the metre reading for submergence at 190 degrees and 10 degrees.
- Depending upon the situation, some submarines may be ordered to search the foreshores after the second day.
Note: The reconnaissance aircraft overturned on landing but no casualties reported.