Attack On Sydney Harbour - Prelude

Prelude

The Japanese navy used five Ko-hyoteki-class midget submarines in an unsuccessful operation against U.S. battleships during the attack on Pearl Harbor. The navy hoped that upgrades to the submarines, intensified crew training, and the selection of a less well defended target would lead to better results and an increased chance of the crews of the midgets to return alive from their mission. Therefore, on 16 December 1941, the navy initiated plans for a second midget submarine operation.

The plans called for two simultaneous attacks against Allied naval vessels in the Indian and South Pacific Oceans. These attacks were intended as diversions ahead of the attack on Midway Island in the North Pacific, with the Japanese hoping to convince the Allies that they intended to attack to the south or west of their conquests. Eleven submarines of the 8th 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 . The submarine groups were to select a suitable port of attack, based on their own reconnaissance.

The Western Attack Group selected the port of Diégo-Suarez in Madagascar. This attack—which occurred at nightfall on 30 May and resulted in the damaging of the battleship HMS Ramillies and the sinking of the tanker British Loyalty—came 22 days after the British captured the port from Vichy France at the beginning of the Battle of Madagascar.

The four potential targets for the Eastern Attack Group were Nouméa, Suva, Auckland, and Sydney. 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 long tons (5,217 t) Russian merchant vessel Wellen, 30 mi (26 nmi; 48 km) from Newcastle, 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 Dutch light cruiser HNLMS Tromp, Australian destroyer HMAS Arunta and U.S. destroyer USS Perkins, searched unsuccessfully for the submarine. Muirhead-Gould concluded 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 authorities dismissed its report as a glitch, as there were no Allied aircraft operating over Sydney. The aircraft was damaged or destroyed on landing, although its two crew survived. They 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 signals intelligence network partially intercepted, resulted in the Japanese navy selecting Sydney as the target. The three midget-carrying submarines rendezvoused with I-29 and I-21 approximately 35 mi (30 nmi; 56 km) north-east of Sydney Heads, with all five submarines in position by 29 May.