Multibeam sonar scan of HMAS Sydney main wreck.  

On 19th November 1941, the pride of the Australian Navy, HMAS Sydney II, a state of the art cruiser that had already won several battles, disappeared in home waters off the Western Australian coast. 75 years on, surveys from the oceans depths are beginning to unravel what happened that fateful day.

In four days of operation in early May 2015, approximately 500,000 still images and 300 hours of video material were gathered from the wrecks of both Sydney and Kormoran, as well as the extensive debris fields surrounding them. In addition, a multi beam sonar scan was made of the main wreck sites, and part of each debris field. Samples of water, soil and marine growth were also taken from the wreck sites to contribute to the management plan that the Western Australian Museum will develop to monitor and protect the sites.

DOF Subsea’s brand new subsea operations vessel.

The primary objective of the mission, however, was to use the wealth of material gathered to uncover the truth about the fate of the two ships, and Andrew Hutchison of Curtin University’s School of Art and Design was determined to humanise the story. As part of the preparations for the mission, he interviewed two men, both in their nineties, who had long service on HMAS Sydney, and who were transferred off Sydney just before she sailed from Fremantle, never to return.

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“I was really struck by how they both talked about the ship as a community, a small town, in which they had lived in the closest of quarters with 600 other guys,” said Dr Hutchison of the two veterans Jim Lavender and Tom Fisher. “Both Jim and Tom were a wealth of information about exactly what parts of the ship did what.

“Their personal stories strongly informed our task planning about which parts of the ship we would focus on.”

Both of the veterans, Jim Lavender and Tom Fisher, have since passed away.

Walking in their shoes

Distributed throughout the debris field, mixed up with shredded steel and cables, torpedoes and gun shells, are dozens, possibly hundreds of shoes. While the natural forces of the ocean have long ago consumed any human remains and clothing, shoes have survived. It is thought that the tanned leather is poisonous to the marine life that can consume even untreated wood.

Two shoes lay on the seafloor at 2,500 meter in the Sydney debris field.

“Shoes are so personal, so we are very interested in them as a way to really convey to an audience just how human this tragedy has been. They really show the human presence that was once there.”

An objective of the project will be to merge the 2008 image set with the 2015 image set to create an integrated superset that becomes a single, interactive site map that shows as much as is known of the wreck sites. This can then be used by marine scientists, archaeologists, and also for presentation to a wider audience.

The problem of accurately establishing scale across the two data sets and different camera types will be accomplished using the wreckage in the debris field itself. Sydney had anti-aircraft guns that used mass produced brass shell casings, many of which are scattered throughout the debris field. Brass is completely resistant to corrosion in seawater, so they provide a very convenient scale bar of known size at many points. Fortunately, the project has access to a brass shell casing of that exact type, in the collection of researcher Wes Olson.

The visual data is already being used to undertake comparisons to the 2008 imagery, to see how the wrecks have changed in only seven years.  The rate of growth of marine life was much faster than many of the team expected.

“I am glad we went back when we did, as the ships are currently still recognisable,” said Hutchison. “But that may not be the case in another 20 years.”

Getting a fix

The problems of fixing location underwater were significant. Very accurate underwater positions on a site can be achieved using Long Base Line system, but this involves the fixing of multiple beacons to the sea floor, a time consuming process in itself. With very limited sea time, LBL was not an option open to the expedition. The alternative was to use ship based acoustic systems to listen to beacons on the ROVs themselves, but this becomes very complex, especially under 2,500 meters of water.

Marine rusticles are quickly covering many part of the ship. 2008 on the left, 2015 on the right.

Inaccuracies can occur due to variations in water depth, temperature and salinity, as well as the motion of the vessel on the surface. Nevertheless, useful position data was achieved for each of the ROVs, and one of the ROVs was equipped with a multi-beam sonar. This has already revealed more detail of the impact craters formed when the ships collided with the seafloor, revealing the angles of decent and great speed they were travelling at, adding to the story of what happened.

It is possible that future technologies such as underwater laser scanning may be able to resurvey the wrecks sites at much less cost, and record in much higher resolution, and the work already done in 2008 and 2015 will provide base lines for the changes that are ongoing in the wreck sites.

“The technology we got to use is amazing, but what really made all that technology come together in one place, at one time, was the huge investment by corporations, specialist suppliers, government agencies, and individuals who donated their time for huge discounts, or even for free, and still treat it as the most urgent priority they had,” said Hutchison. “It is a very powerful story that everyone wanted to see brought to light.”