Numerous attempts were made to find the Australian cruiser HMAS Sydney and the German auxiliary cruiser Kormoran, which were both lost in a sea battle in 1941. Efforts immediately after the battle focused on finding Sydney when she failed to return to port. While searchers located over 300 survivors from Kormoran, none of the 645 aboard the Australian warship were found. In March 2008, shipwreck hunter David Mearns commenced a search for the two wrecks. Kormoran was located on 12 March in close proximity to the sinking position given in German accounts. Using the survivor's information on Sydney's last known heading, Mearns and his search team located Sydney on 17 March.

Post-war searches attempted to find one or both of the combatants, but were unsuccessful because of a lack of detailed information about the battle's location. Searchers distrusted the German survivors and their accounts; the large difference between the number of survivors from each ship prompted theories that Kormoran's crew had acted illegally during the battle and were attempting to cover up their actions. As a result, hypotheses about the wrecks' locations varied from deep water many kilometres off Dirk Hartog Island, to sites nearer to Carnarvon, Western Australia, and as far south as the western side of the Houtman Abrolhos Islands.

Mearns had previously been involved in the discovery of the cargo ship Lucona (the key evidence in the arrest of Udo Proksch for murder and insurance fraud), the bulk carrier Derbyshire (the largest British ship to be lost at sea), and the battlecruiser HMS Hood.^[15] He first learned of the battle and mutual destruction of Sydney and Kormoran during a conference in 1996, and started studying the battle in 2001 with a view to finding the ships.^[16]

With the assistance of other historians and the Western Australian Museum, Mearns researched the battle, focusing on primary source documents. He discovered several archive files and Kormoran diaries previously believed to be lost.^[17] His research led Mearns to believe that the German accounts were accurate.^[18] After two failed attempts to attract the attention and support of the Royal Australian Navy, Mearns was informed in January 2004 that the navy was reconsidering its stance.^[19] At this point Mearns and his company entered a partnership and drew up a memorandum of understanding with HMAS Sydney Search Pty Ltd.^[20] In mid-September 2004 Mearns received approval from the German government to film Kormoran if she was found.^[21]

On 14 August 2005 the Australian government announced a A$1.3 million funding grant to the Finding Sydney Foundation, the charitable foundation set up in 2003 by the directors of HMAS Sydney Search, which was quickly followed by a A$500,000 contribution from the Western Australian government and a A$250,000 grant from the government of New South Wales.^[22] Several small donations were made by companies and the public, but plans to search for the ships were on hold until the Australian government approved another A$2.9 million in funds in October 2007.^[23][24]

Mearns planned to determine a 'search box' for Kormoran by plotting possible starting points of its two lifeboats through a reverse drift analysis.^[25] Previous drift analyses had focused on the lifeboat that had made landfall, as the officer in charge had maintained a log of the boat's progress. These analyses provided widely-spread results because the log was incomplete and eddy currents which would have affected the course and speed of the lifeboat were rarely accounted for. The lifeboat would have been affected by oar and sail power in addition to ocean currents, and most researchers focused on deriving a specific point from the analysis instead of determining a general search area.^[26] The search box (which was 52 by 34 nautical miles (96 by 63 km; 60 by 39 mi) in size) would be inspected over the course of several days with a towed deep-water side-scan sonar.^[27] Mearns chose to focus on finding Kormoran first, as locating the German ship would significantly narrow down the search area for Sydney and improve the chances of finding it.^[25] After locating one or both vessels, the search ship would return to port and replace the sonar with a remotely operated vehicle (ROV) to photograph and video the wrecks.^[28]

The survey vessel SV Geosounder was chartered from the subsea exploration company DOF Subsea Australia; in addition to being the best of several vessels considered, Geosounder was the only ship with the required capabilities available for hire during the search period.^[29] Mearns had only enough funding to hire and operate Geosounder for 45 days.^[30] Geosounder was scheduled to depart early on 29 February, but a series of problems requiring last-minute modifications delayed departure until after 16:00, and the ship had to return to port that evening because of a fuel leak.^[31] Repairs were made, and the ship reached the south-east corner of Mearns' search box just before midnight on 4 March.^[32] Searchers were hampered by recurring problems with the side-scan sonar and the occurrence of Tropical Cyclone Ophelia in the early days of the expedition.^[33] Kormoran was located at 26°05′46″S 111°04′33″E during the afternoon of 12 March 2008. It was 2,560 metres (8,400 ft) below sea level, with two large pieces 1,300 metres (4,300 ft) apart and an oval-shaped debris field in between.^[34] The raider's discovery was publicly announced by Australian Prime Minister Kevin Rudd on the morning of 17 March.^[35]

Kormoran

Sydney

Carnarvon

Location of the two wrecks off Shark Bay

Using the newly discovered wreck and German accounts describing Sydney's heading, speed, and last sighting after the battle, a 20 by 18 nautical miles (37 by 33 km) search box for the cruiser was calculated.^[36] The dramatic difference in the size of the search boxes was because the German raider's location had been recounted by survivors only as a broad latitude and longitude, while much information was available concerning the Australian cruiser's position relative to the raider.^[36] Sydney was located on 17 March just after 11:00, only hours after Kormoran's discovery was publicly announced.^[37] News that the cruiser had been found was made public the next day in another official announcement by Prime Minister Rudd.^[38] Sydney's wreck was located at 26°14′31″S 111°12′48″E in 2,468 metres (8,097 ft) of water; the bow of the cruiser, which had broken off as the ship sank, was located at the opposite end of a debris field stretching less than 500 metres (1,600 ft) north-west from the hull.^[39][40] The wrecks were 11.4 nautical miles (21.1 km) apart, with Sydney south-east of Kormoran.^[41] On discovery, both wrecks were placed under the protection of the Historic Shipwrecks Act 1976, which penalises anyone disturbing a protected shipwreck with a fine of up to A$10,000 or a maximum five years imprisonment.^[42]

Geosounder returned to Geraldton on 20 March. Major delays during the installation and testing of the ROV delayed departure until 29 March, with the survey ship sailing through the path of Cyclone Pancho.^[43] Electrical problems with the ROV pushed the start of filming back to 3 April. Sydney was the first to be inspected,^[44] with six ROV dives over a five-day period, during which the main hull and debris field were filmed and documented.^[45] The bow had torn free, causing the ship to sink; the main hull section had hit the seabed stern first.^[46] This damage corresponded with descriptions given by the Kormoran' crew after the battle.^[47] Geosounder next travelled to the wreck of Kormoran.^[48] The ship had been split into two large pieces by the explosion of the mine deck, which also destroyed the superstructure and scattered debris across a wide area.^[48] A possible battle site was located during the sonar search, but observation with the ROV revealed that what was thought to be debris from the ships were actually outcrops of pillow lava.^[49]

The search was declared complete just before midnight on 7 April; Geosounder returned to Geraldton.^[50] In November 2009 the Finding Sydney Foundation donated more than 1,400 photographs and 50 hours of video of the wrecks to the Australian War Memorial.^[51]