The NSW Government continues to work collaboratively with the Commonwealth and Japanese governments to protect this highly significant site. Wreck of the midget submarine M For over 60 years one of the greatest Australian wartime and maritime mysteries was the whereabouts of the third and last Japanese midget submarine, which invaded Sydney Harbour on the evening of 31 May
At A. Uttrick peered through his binoculars from the deck of the minesweeper USS Condor. By the pale light of a waning moon, the American sailor spied something unusual piercing the glassy skin of the Pacific Ocean less than two miles south of the entrance to Pearl Harbor.
On the night of 29 Mayfive large Japanese submarines positioned themselves 56 kilometres north-east of Sydney Heads. After circling Sydney Harbour the aircraft returned to its submarine, reporting the presence of 'battleships and cruisers' moored in the harbour. The flotilla's commanding officer decided to attack the harbour with midget submarines the next night.
A midget submarine also called a mini submarine is any submarine under tons,  typically operated by a crew of one or two but sometimes up to 6 or 9, with little or no on-board living accommodation. They normally work with mother ships, from which they are launched and recovered and which provide living accommodation for the crew and support staff. Both military and civilian midget submarines have been built.
Contributor: David Stubblebine. By definition, a midget submarine is less than tons, has a crew of no more than eight, has no on-board living accommodation, and operates in conjunction with a mother ship to provide the living accommodations and other support. The Japanese Navy built at least midgets in 7 classes, but only a fraction had any noticeable impact on the war.
They had hull numbers but no names. For simplicity, they are most often referred to by the hull number of the mother submarine. Thus, the midget carried by I -class submarine was known as I's boat, or "Itou.
It was substantially larger than the original Chariot manned torpedo. Known individually as X-Craftthe vessels were designed to be towed to their intended area of operations by a full-size 'mother' submarine - usually one of the T class or S class - with a passage crew on board, the operational crew being transferred from the towing submarine to the X-Craft by dinghy when the operational area was reached, the passage crew returning with the dinghy to the towing submarine. Once the attack was over, the X-Craft would rendezvous with the towing submarine and then be towed home.
As part of the attack on Pearl Harbor on December 7,the Imperial Japanese Navy sent an attack group of submarines to surround Oahu and sink ships attempting to flee. Five of the submarines carried top-secret "mini submarines. They were to surface and fire their torpedoes during the aerial attack. Then, they would dive and escape the harbor, and rendezvous with their "mother submarines," again under cover of darkness the night of December 7.
On 29 May five large Japanese I- class submarines rendezvoused some 35 nautical miles northeast of the entrance to Sydney Harbour. Before daylight the next morning an E14Y Glen float plane launched from one of the submarines, Iand crewed by Warrant Flying officer Susumo Ito and Ordinary Seaman Iwasaki, flew a daring reconnaissance mission over the harbour, twice circling the cruiser USS Chicago before flying off to the east. The aerial intrusion was observed and reported but it did not initiate any special harbour defensive measures being implemented.
They were the smallest submarines in the Kriegsmarine. The Biber was hastily developed to help meet the threat of an Allied invasion of Europe. This resulted in basic technical flaws that, combined with the inadequate training of their operators, meant they never posed a real threat to Allied shipping, despite submarines being delivered.