page_title: Attack on Sydney Harbour
section_title: Flaws in Japanese tactics
hierarchical_section_title: Attack on Sydney Harbour / Analysis / Flaws in Japanese tactics
caption_attribution_description: Japanese midget submarine M-21 being raised from Sydney Harbour by a floating crane.
context_page_description: In late May and early June 1942, during World War II, submarines belonging to the Imperial Japanese Navy made a series of attacks on the cities of Sydney and Newcastle in New South Wales, Australia. On the night of 31 May – 1 June, three Ko-hyoteki-class midget submarines, each with a two-member crew, entered Sydney Harbour, avoided the partially constructed Sydney Harbour anti-submarine boom net, and attempted 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 submarine, whilst m-21 was successfully attacked and sunk. The crew of M-21 killed themselves. These submarines were later recovered by the Allies. The third submarine attempted to torpedo the heavy cruiser USS Chicago, but instead sank the converted ferry HMAS Kuttabul, killing 21 sailors. This midget submarine's fate was unknown until 2006, when amateur scuba divers discovered the wreck off Sydney's northern beaches.
  Immediately following the raid, the five Japanese fleet submarines that carried the midget submarines to Australia embarked on a campaign to disrupt merchant shipping in eastern Australian waters.
context_section_description: 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 carrier-supported aerial combat. As a result, the midget program'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 midgets had no effect, and tying up 11 large submarines for six weeks in support of further midget submarine attacks on Sydney and Diego Suarez proved a waste of resources.
  Moreover, the failures at Sydney Harbour and Diego Suarez demonstrated that the improvements to the midget submarines made after Pearl Harbor had not increased the overall impact of the midget program. The modifications had various effects. The ability to man and deploy the midgets while the mother ships were submerged prevented the Army coastal radars from detecting the mother submarines. However, the midgets were still difficult to control, unstable, and prone to surfacing or diving uncontrollably. These manoeuvrability issues contributed to M-14's entanglement in the anti-submarine net, and the repeated detection of M-21 and M-24.
  Beyond the use of the unreliable midgets, historians have identified areas in the plan of attack where the Japanese could have done significantly more damage. If the Japanese midget submarines had conducted a simultaneous, co-ordinated attack, they would have overwhelmed the defences. A chance for more damage came following the destruction of Kuttabul, when several naval vessels headed to sea, including USS Chicago, USS Perkins, Dutch submarine K-IX, HMAS Whyalla, and HMIS Bombay. The five mother submarines were already en route to the Port Hacking recovery position, and although Sasaki's plan at Pearl Harbor had been to leave some submarines at the harbour mouth to pick off fleeing vessels, he did not repeat this tactic.
caption: M-21 being raised by a floating crane on 10 June 1942
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