The 'Sinking of Centaur', an Australian hospital ship, resulted from an attack by a Japanese submarine off the coast of Queensland in the waters of eastern Australia (14 May 1943).

Of the 332 medical personnel and civilian crew aboard, 268 died, including 63 of the 65 army personnel.

Built in Scotland and launched in 1924 as a combination passenger liner and refrigerated cargo ship for the Blue Funnel Line subsidiary of Alfred Holt & Co. Ltd, Centaur operated the trade route between Western Australia and Singapore via the Netherlands East Indies carrying passengers, cargo and livestock. At the start of World War II, in common with all British merchant marine vessels, Centaur was placed under British Admiralty control, but after being fitted with defensive equipment was allowed to continue normal operations. In November 1941, the ship rescued German survivors of the engagement between the merchant raider Kormoran and the Australian light cruiser Sydney. Centaur was relocated to Australia’s east coast in October 1942, and used to transport matériel to New Guinea.

In January 1943, Centaur was transferred to the Australian military for conversion to a hospital ship, as her small size made her suitable for operating in the waters of South-East Asia. The refit included the installation of medical facilities and repainting with Red Cross markings, and was completed in March. The ship then undertook a trial voyage transporting wounded from Townsville to Brisbane, then from Port Moresby to Brisbane. After replenishing in Sydney, Centaur embarked the 2/12^th Field Ambulance for transport to New Guinea, and sailed on 12 May. Before dawn on 14 May 1943, during her second voyage, Centaur was torpedoed and sunk by a Japanese submarine off Moreton Island, Queensland. The majority of the 332 aboard died in the attack, 64 survivors being discovered 36 hours later. The incident resulted in public outrage as attacking a hospital ship is considered a war crime under the 1907 Hague Convention. Protests were made by the Australian and British governments to Japan and efforts were made to discover the people responsible so they could be tried at a war crimes tribunal.

As noted above, at the beginning of 1943 Centaur was placed at the disposal of the Australian Department of Defence for conversion to a hospital ship. The conversion was performed by United Ship Services in Melbourne, Australia, and was initially estimated to cost £20,000. The cost increased to almost £55,000 for a variety of reasons. It was originally intended for the ship to operate between ports in New Guinea and Townsville in Queensland, but increasing casualty numbers in the New Guinea campaign meant that the hospitals in Queensland would quickly become unable to deal with the quantity of the casualties and the nature of their injuries, so a longer voyage to Sydney was required. The army demanded that more facilities and conversions be added to the original plans such as expanded bathing and washing facilities, hot water made available to all parts of the ship, the rerouting of all steam pipes away from patient areas, and ventilation arrangements suitable for tropical conditions. 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.

As relaunched on 12 March 1943, Centaur was equipped with an operating theatre, a dispensary, two wards on the former cattle decks and a dental surgery, along with quarters for 75 crew and 65 permanent army medical staff. To maintain the ship’s mean draught of 20 ft (6.1 m), 900 tons of ironstone were distributed through the cargo holds as ballast. Centaur was capable of voyages of 18 days before needing resupply, and could carry just more than 250 bed-ridden patients.

With the start of hostilities between Japan and the British empire, it became clear that the three hospital ships currently serving Australia (Manunda, Wanganella and Oranje) would be unable to operate in the shallow waters typical of South-East Asia, so a new hospital ship was required. As none of the Australian merchant marine vessels able to operate in this region was suitable for conversion to a hospital ship, a request to the British Ministry of Shipping resulted in the placement of Centaur at the disposal of the Australian military on 4 January 1943, conversion work began on 9 January and Centaur was commissioned as an Australian hospital ship on 1 March: during her conversion, Centaur was painted with the markings of a hospital ship as detailed in Article 5 of the 10^th Hague Convention of 1907 ('Adaptation to Maritime War of the Principles of the Geneva Convention') with a white hull with a green band interspersed by three red crosses on each beam, white superstructure, many 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. At night, the markings were illuminated by a combination of internal and external lights.Data on the ship’s markings and the layout of identifying structural features was provided in the first week of February 1943 to the International Committee of the Red Cross, which passed passed them on to the Japanese on 5 February. This information was also circulated and promoted by the press and media.

Centaur entered service as a hospital ship on 12 March 1943, and the early stages of the 'new' ship’s first voyage as a hospital ship were test and transport runs: the initial run from Melbourne to Sydney resulted in the master, chief engineer and chief medical officer composing a long list of defects requiring attention. Following repairs, Centaur undertook a test run, transporting wounded servicemen from Townsville to Brisbane to ensure that she was capable of fulfilling the role of a medical vessel. Centaur was then tasked with delivering medical personnel to Port Moresby, New Guinea, and returning to Brisbane with Australian and US wounded along with a few wounded Japanese prisoners of war.

Arriving in Sydney on 8 May 1943, Centaur was reprovisioned at Darling Harbour before departing for Cairns, Queensland on 12 May 1943. From there, her destination was again New Guinea. On board at the time were 74 civilian crew, 53 Australian Army Medical Corps personnel (including eight officers), 12 female nurses from the Australian Army Nursing Service, 192 soldiers of the 2/12^th Field Ambulance, and one Torres Strait ship pilot. Most of the female nurses had transferred from the hospital ship Oranje, and the male army personnel assigned to the ship were all medical staff. During the loading process, there was an incident when the ambulance drivers attached to the 2/12^th attempted to bring their rifles and personal supplies of ammunition aboard: this was met with disapproval by Centaur's master and chief medical officer, and raised concerns among the crew and wharf labourers that Centaur would be transporting military supplies or commandos to New Guinea. The rifles were not allowed on board until Centaur's master had received official reassurance that the ambulance drivers were allowed to carry weapons under the 10^th Hague Convention (specifically Article 8), as they were used 'for the maintenance of order and the defence of the wounded'. The remaining cargo was searched by the crew and labourers for other weapons and munitions.

At about 04.10 on 14 May, in the course of her second run from Sydney to Port Moresby, Centaur was torpedoed by an unsighted submarine. The torpedo struck the port-side oil fuel tank approximately 6 ft 7 in (2 m) below the waterline, the warhead’s detonation blasting a hole 26 to 33 ft (8 to 10 m) wide, igniting the fuel and setting the ship on fire from the bridge aft. Many of those on board were killed very quickly by concussion or perished in the inferno. Centaur quickly took on water through the hole on her side, rolled to port and then sank bow-first, going under in less than three minutes. The rapid sinking prevented the deployment of lifeboats, although two broke off as Centaur, along with several damaged liferafts.

According to the position extrapolated by Second Officer Gordon Rippon from the 04.00 dead reckoning position, Centaur was attacked about 28 miles (44 km) to the east-north-east of Point Lookout, North Stradbroke Island, Queensland. 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 being located within 1.2 miles (1.9 km) of Rippon’s co-ordinates.

Of the 332 persons on board, just 64 were rescued. Most of the crew and passengers had been asleep at the time of the attack and had be afforded only a minimal chance to escape. It was estimated that up to 200 persons may have been alive at the time Centaur wet under. Several who made it off the ship later died from fragmentation wounds or burns, and others were unable to find support and drowned. The survivors spent 36 hours in the water using barrels, wreckage, and the two damaged lifeboats for flotation. During this time, they drifted about 22.6 miles (36.3 km) to the north-east of Centaur's calculated point of sinking and spread out over an area of 2.3 miles (3.7 km). The survivors saw at least four ships and several aircraft, but could not attract their attention. At the time of their rescue, the survivors were in two large and three small groups, with several more floating alone.

On the morning of 15 May 1943, the US destroyer Mugford departed Brisbane to escort the 11,063-ton New Zealand freighter Sussex on the first stage of the latter’s passage across the Tasman Sea. At 14.00, one of the destroyer’s look-outs reported an object on the horizon. At about the same time, an Avro Anson twin-engined coastal reconnaissance aeroplane of the Royal Australian Air Force’s No. 71 Squadron, flying ahead on anti-submarine watch, dived toward the object. The aircraft returned to the two ships and signalled that there were shipwreck survivors in the water requiring rescue. Mugford's commanding officer ordered Sussex to continue alone as the destroyer recovered the survivors. Marksmen were positioned around the ship to shoot sharks, and sailors stood ready to dive in and assist the wounded. Mugford's medical personnel inspected each person as they came aboard and provided necessary medical care, and the US crew learned from the first group of survivors that they were from the hospital ship Centaur.

At 14.14, Mugford contacted the naval officer in charge in Brisbane to report that the ship was recovering survivors from Centaur: this was the first that anyone in Australia had knowledge of the attack. The rescue of the 64 survivors took 80 minutes, although Mugford remained in the area until dark as she searched for more survivors. After the fall of night, Mugford returned to Brisbane, arriving shortly before 00.00. Further searches of the waters off North Stradbroke Island were made by the US destroyer Helm during the night of 15 May until 06.00 on 16 May, and by the Australian corvette Lithgow and four motor torpedo boats from 16 to 21 May, neither search finding more survivors.

At the time of the attack, none aboard Centaur saw what had attacked the ship. As a result of the ship’s position, the distance from shore and the depth of the water, it was concluded that she was torpedoed by one of the Japanese submarines known to be operating off the Australian eastern coast: several survivors later claimed to have heard the attacking submarine moving on the surface while they were adrift, and the submarine was seen by the ship’s cook, who was floating alone on a hatch cover, out of sight from the main cluster of survivors. The latter described the submarine to Naval intelligence following the survivors' return to land, and his description matched the profile of a 'Kaidai' class fleet submarine of the Imperial Japanese navy.

At the time of the attack, three 'Kaidai' class boats were operating off Australia’s eastern coast: these were I-177 under the command of Lieutenant Commander Hajime Nakagawa, I-178 under the command of Lieutenant Commander Hidejiro Utsuki, and I-180 under the command of Lieutenant Commander Toshio Kusaka. None of these submarines survived the war: I-177 was sunk by the US Samuel S. Miles on 3 October 1944, I-178 by the US Patterson on 25 August 1943 and I-180 by the US Gilmore on 26 April 1944. Kusaka and Nakagawa had been transferred to other submarines before the loss of I-180 and I-177 respectively, but Utsuki and I-178 were sunk while returning from the patrol off the coast of Australia.

In December 1943, following official protests, the Japanese government issued a statement formally denying responsibility for the sinking of Centaur. Records provided by the Japanese following the war also did not acknowledge responsibility. Although Centaur's sinking was a war crime, no one was tried for sinking the hospital ship. Investigations into the attack were undertaken between 1944 and 1948, and included the interrogation of the commanders of the submarines operating in Australian waters at the time, their superiors and junior officers and crewmen from the submarines who had survived the war. Several of the investigators suspected that Nakagawa and I-177 were most likely responsible, but they were unable to establish this beyond reasonable doubt, and the Centaur case file was closed on 14 December 1948 without any charges laid.

In 1972, the German naval historian Jürgen Rohwer claimed in Chronology of the War at Sea that it was I-177 which had torpedoed Centaur, based on a Japanese report stating that I-177 had attacked a ship on 14 May 1943 in the area in which the hospital ship had been sunk. The 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. As an official history of the Japanese navy, Sakamoto’s work was considered to be official admission of the attacking submarine’s identity, and most sources subsequently assumed as fact Nakagawa’s and I-177's role in the sinking of Centaur. Nakagawa, who died in 1991, refused to speak about the attack on Centaur following the war crimes investigation at the end of World War II or even to defend himself or deny the claims made by Rohwer and Sakamoto.

The attack was universally condemned by Australian servicemen, who commonly believed that the attack on Centaur had been carried out deliberately and in full knowledge of her status. Similar reactions were expressed by other Allied personnel.

Six days after the sinking of Centaur, the Australian Department of Defence requested that the identification markings and lights be removed from the Australian hospital ship Manunda, weapons be installed, and that operate blacked out and under escort. The conversion was performed, although efforts by the Department of the Navy, the Admiralty, and authorities in New Zealand and the USA caused the completed conversion to be undone. The cost of the roundabout work came to £12,500, and kept Manunda out of service for three months. On 9 June 1943, communications between the Combined Chiefs-of-Staff on the subject of hospital ships contained a section referring to the Manunda incident as a response to the attack on Centaur, with the conclusion that the attack was the work of an irresponsible Japanese commander, and that it would be better to wait until further attacks had been made before considering the removal of hospital ship markings.

After consultation with the Australian armed forces, General Douglas MacArthur, the Admiralty and the Australian government, an official protest was sent. This was received by the Japanese government on 29 May 1943, and at about the same time, the International Committee of the Red Cross sent a protest on behalf of the major Allied Red Cross organisations to the Japanese Red Cross. On 26 December 1943, a response to the Australian protest arrived. It stated that the Japanese government had no information justifying the allegation made, and therefore took no responsibility for what happened. The reply counter-protested that nine Japanese hospital ships had been attacked by the Allies, although these claims were directed against the USA rather than Australia. Although several later exchanges were made, the lack of progress saw the British government inform the Australian prime minister on 14 November 1944 that no further communications would be made on the loss of Centaur.

After World War II, several searches of the waters around North Stradbroke and Moreton Islands failed to reveal Centaur's location. It was believed that she had sunk off the edge of the continental shelf, to a depth at which the Royal Australian Navy lacked the capability to search for a vessel of Centaur's size.

In 1995, it was announced that the wreck of Centaur had been located in waters 10 miles (17 km) from the lighthouse on Moreton Island, a significant distance from her believed last position. The finding was reported on 'A Current Affair', during which footage of the shipwreck, 560 ft (170 m) underwater, was shown. The discoverer, Donald Dennis, claimed the identity of the wreck had been confirmed by the Navy, the Queensland Maritime Museum, and the Australian War Memorial. A cursory search by the navy confirmed the presence of a wreck at the given location, which was gazetted as a war grave and added to navigation charts by the Australian Hydrographic Office.

Over the next eight years, there was growing doubt about the position of Dennis’s wreck. During this time, Dennis had been convicted on two counts of deception and one of theft through scams. Two wreck divers, Trevor Jackson and Simon Mitchell, used the location for a four-hour world record dive on 14 May 2002, during which they examined the wreck and took measurements, claiming that the ship was too small to be Centaur. Jackson had been studying Centaur for some time, and believed that the wreck was actually another, much smaller ship, the 180-ft (55-m) motor vessel Kyogle, a lime freighter purchased by the Royal Australian Air Force and sunk during bombing practice on 12 May 1951. 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'.

On the 60^th anniversary of the sinking, '60 Minutes' ran a story demonstrating that the wreck was not Centaur. It was revealed that nobody at the Queensland Maritime Museum had yet seen Dennis’s footage, and when it was shown to the museum’s Rod McLeod and a maritime historian, they stated that the wreck could not be Centaur as a result of physical inconsistencies, such as an incorrect rudder. Following this story, and others published around the same time in newspapers, the navy sent three ships to inspect the site over a two-month period, before concluding that the wreck had been incorrectly identified as Centaur.

In April 2008, following the discovery of the wreck of the light cruiser Sydney, several parties began calling for a dedicated search for Centaur, and by the end of 2008 the Australian federal and Queensland state governments had formed a joint committee and contributed A$2 million each toward a search, and tenders to supply equipment (including the search vessel, side-scan sonar systems and a remotely operated inspection submersible) were opened in February 2009, and awarded during the year. The search, conducted from the Defence Maritime Services vessel Seahorse Spirit began during the weekend of 12/13 December 2009. The initial search area off Cape Moreton covered 527 sq miles (1365 km²), the search team being given 35 days to locate and film the wreck before funding was exhausted.

Six sonar targets with dimensions similar to those of Centaur were located between 15 and 18 December: as none of the contacts corresponded completely to the hospital ship, the search team opted to take advantage of favourable weather conditions and continue investigating the area before returning to each site and making a detailed inspection with a higher-resolution sonar. On the afternoon of 18 December, the sonar towfish separated from the cable, and was lost in 5,900 ft (1800 m) of water, forcing the use of the high-resolution sonar to complete the area search. After inspecting the potential targets, the search team announced on 20 December that it had found Centaur that morning at a depth of 6,755 ft (2059 m) less than 1.2 miles (1.9 km) from Rippon’s co-ordinates. The wreck site has since been marked as a war grave and protected with a navigational exclusion zone under the Historic Shipwrecks Act 1976.