In January 1943, Centaur was handed over to the Australian military for conversion to a hospital ship, as her small size made her suitable for operating in Maritime Southeast Asia.
In early 1923, the Ocean Steamship Company (a subsidiary of Alfred Holt's Blue Funnel Line) decided that a new vessel would be required to replace the ageing Charon on the Western Australia to Singapore trade route.
[15] The unions representing the ship's crew requested improved living and dining conditions, including new sinks in the food preparation areas and the replacement of flooring in the quarters and mess rooms.
[15] When AHS Centaur was relaunched on 12 March 1943, she was equipped with an operating theatre, dispensary, two wards (located on the former cattle decks), and a dental surgery, along with quarters for seventy five crew and sixty five permanent Army medical staff.
[19] Centaur's route ran from Fremantle up the Western Australian coast calling at Geraldton, Carnarvon, Onslow, Point Samson, Port Hedland, Broome, and Derby[20] then to the Bali Strait, Surabaya, Semarang, Batavia, and Singapore.
[22] Kyo Maru II had developed boiler problems while returning from the Antarctic and was drifting towards the Houtman Abrolhos Archipelago, where she was in danger of being wrecked by the reefs in the area.
[28] On arrival in Carnarvon, the Germans were relocated to the number one cargo hold, where they were joined by another hundred Kormoran survivors collected by other ships, plus forty Australian Army guards, which were then transported by Centaur to Fremantle.
[30] During her conversion, Centaur was painted with the markings of a hospital ship as detailed in Article 5 of the tenth Hague Convention of 1907 ("Adaptation to Maritime War of the Principles of the Geneva Convention");[31] white hull with a green band interspersed by three red crosses on each flank of the hull, white superstructure, multiple large red crosses positioned so that the ship's status would be visible from both sea and air, and an identification number (for Centaur, 47) on her bows.
[36] Following repairs, she conducted a test run, transporting wounded servicemen from Townsville to Brisbane to ensure that she was capable of fulfilling the role of a medical vessel.
[51][52] Doubts were initially cast on the accuracy of both the calculated point of sinking and the dead reckoning position, but the 2009 discovery of the wreck found both to be correct, Centaur located within 1 nautical mile (1.9 km; 1.2 mi) of Rippon's coordinates.
[62][63] On the morning of 15 May 1943, the American destroyer USS Mugford departed Brisbane to escort the 11,063 ton New Zealand freighter Sussex on the first stage of the latter's trans-Tasman voyage.
[79][80] Japanese Rear Admiral Kaneyoshi Sakamoto, who had shown Rohwer the report, stated that Nakagawa and I-177 were responsible for the attack on Centaur in his 1979 book History of Submarine Warfare.
[71][82] The media were notified of Centaur's sinking on 17 May 1943, but were ordered not to release the news until it had been announced in the South West Pacific Area's General Headquarters dispatch at midday on 18 May, and in Parliament by Prime Minister John Curtin that afternoon.
[88] Politicians urged the public to use their rage to fuel the war effort, and Centaur became a symbol of Australia's determination to defeat what appeared to be a brutal and uncompromising enemy.
[92] Similar reactions were expressed by other Allied personnel; United States Army Air Forces General George Kenney recalled having to talk a sergeant bombardier out of organising a retaliatory bombing run on a Japanese hospital ship known to be in their area.
[96] When the consideration was made that the ambulance drivers' weapons incident just before Centaur's voyage may have been partially responsible for the attack, it led to the tightening of rules regarding who was allowed to travel on a hospital ship.
[102] Centaur's Master, believing he had been given a route intended for a merchant vessel, set a course closer to land, but on the seaward side of 2,000 metres (6,600 ft) in depth.
[110] This theory states that Nakagawa was fully aware that his target was a hospital ship and decided to sink her regardless, either on his own initiative or on a poor interpretation of his orders.
[39] Other claims include that Nakagawa may have been acting in vengeance for casualties inflicted by the Allies during the Battle of the Bismarck Sea, or may have expected praise for the sinking of an enemy naval vessel.
[113] His defence, that he was acting under orders from Vice Admiral Shiro Takasu, was not accepted, and he was sentenced to four years imprisonment at Sugamo Prison as a Class B war criminal.
[114] In 1974, two divers claimed to have found the ship approximately 40 nautical miles (74 km; 46 mi) east of Brisbane, in 60 metres (200 ft) of water, but did not disclose its exact location.
[116] In 1995, it was announced that the shipwreck of Centaur had been located in waters 9 nautical miles (17 km; 10 mi) from the lighthouse on Moreton Island, a significant distance from her believed last position.
[117] A cursory search by the Navy confirmed the presence of a shipwreck at the given location, which was gazetted as a war grave and added to navigation charts by the Australian Hydrographic Office.
[1][117] Over the next eight years, there was growing doubt about the position of Dennis' wreck, due to the distance from both Second Officer Rippon's calculation of the point of sinking and where USS Mugford found the survivors.
[119] Jackson had been studying Centaur for some time, and believed that the wreck was actually another, much smaller ship, the 55-metre-long (180 ft) MV Kyogle, a lime freighter purchased by the Royal Australian Air Force and sunk during bombing practice on 12 May 1951.
[117][119] The facts gathered on the dive were inconclusive, but the divers remained adamant it was not Centaur, and passed this information onto Nick Greenaway, producer of the newsmagazine show 60 Minutes.
[121][122][123] The search, conducted from the Defence Maritime Services vessel Seahorse Spirit and overseen by shipwreck hunter David Mearns, commenced during the weekend of 12–13 December 2009.
[132] In 1990, a stained glass memorial window depicting Centaur, along with a plaque listing the names of those lost in the attack, was installed at Concord Repatriation General Hospital, at a cost of A$16,000.
[129] This would normally be a breach of the Historic Shipwrecks Act, but a special dispensation permitted the manoeuvre, as placing the plaque on the seabed next to the ship would have seen it sink into the sediment.
[129] Following the ship's discovery, a national memorial service at St John's Cathedral, Brisbane on 2 March 2010 was attended by over 600 people, including Prime Minister Kevin Rudd.