Indian Ocean raid ( 1944 ) In March 1944 , a force of three Imperial Japanese Navy ( IJN ) heavy cruiser s raided Allied shipping in the Indian Ocean . The cruisers departed Japanese - held territory on 1 March with the support of other IJN vessels and aircraft . On 9 March , they encountered and sank the British steamer " Behar " , with the heavy cruiser picking up over 100 survivors . Fearing detection , the Japanese force subsequently returned to the Netherlands East Indies ( NEI ) , arriving on 16 March . Two days later , most of " Behar " s crew and passengers were murdered on board " Tone " . Following the war the commander of the raid , Rear Admiral Naomasa Sakonju , was executed for this war crime and " Tone " s captain Haruo Mayazumi was sentenced to seven years imprisonment . Background . In February 1944 , the Japanese Combined Fleet withdrew from its base at Truk in the Central $ 3 to Palau and Singapore . The appearance of a powerful Japanese naval force at Singapore concerned the Allies , as it was feared that these ships could potentially conduct raids in the Indian Ocean and against Western Australia . In response , the Allies strengthened their naval and air forces in the area by transferring two British light cruiser s from the $ 3 and Mediterranean as well as several U . S . Navy warships from the $ 3 . The number of air units in Ceylon and the Bay of Bengal region was also increased . Admiral James Somerville , the commander of the British Eastern Fleet , feared that the Japanese would repeat their devastating Indian Ocean raid of early 1942 , and on 25 February requested permission to withdraw his fleet from its base at Trincomalee so that it was not at risk from the larger Japanese force . The Admiralty rejected this request , and directed that the fleet should remain at Trincomalee unless it was threatened by a superior Japanese force as its withdrawal would affect morale and harm Britain ' s prestige in the region . It was agreed , however , that the Eastern Fleet should not engage superior Japanese forces and could withdraw if Somerville judged this necessary . In late February , Vice - Admiral Shiro Takasu — the Commander in Chief , South - West Area fleet — ordered the heavy cruisers , , and to raid Allied shipping on the main route between Aden and Fremantle . This force was commanded by Vice Admiral Naomasa Sakonju on board " Aoba " . In his instructions to Sakonju , Vice Admiral Takasu directed that if the force captured Allied merchant seamen all prisoners , other than radio operators and other personnel who might possess useful information , were to be killed . Sakonju did not question this order . The Japanese cruisers embarked specialised boarding parties for this operation as it was hoped that they could capture merchant ships to alleviate Japan ' s shipping shortage . Raid . The three Japanese heavy cruisers departed from the Combined Fleet ' s anchorage in the Lingga Islands on 27 February . The light cruisers and and five destroyers escorted the force through the Sunda Strait on 1 March . The raiders were supported by 10 medium bombers and three or four seaplane s based in Sumatra and west Java which conducted patrols in the direction of Ceylon . Three or four submarines from the 8th Flotilla also monitored Allied shipping movements near Ceylon , the Maldive Islands and Chagos Archipelago . The Allies did not detect the Japanese force ' s departure , but reinforced their forces in Western Australia after an American submarine encountered " Kinu " and " Ōi " operating near the Lombok Strait on 6 March . The presence of these ships was taken to indicate that a raiding force had possibly been dispatched into the Indian Ocean . On 8 March , Somerville directed all Allied ships travelling between 80 and 100° east to divert to the south or west . After leaving the Sunda Strait , the Japanese heavy cruisers sailed south - west for the main route between Aden and Fremantle . The ships were spread by day and by night and maintained radio silence . On the morning of 9 March , they encountered the British steamer " Behar " at , about midway between Fremantle and Colombo . The ship was travelling from Fremantle to Bombay as part of a voyage between Newcastle , New South Wales and the United Kingdom carrying a cargo of zinc . Upon sighting the Japanese ships , " Behar " s master , Captain Maurice Symonds , ordered that that his radio operator transmit the " RRR " code in order to notify other ships and Allied bases that the merchant ship was being attacked by surface raiders . " Tone " s signals room picked up this message , and the cruiser opened fire on " Behar " . The Japanese cruiser did not attempt to capture the steamer , as it was judged too risky to sail her back to Japanese territory . " Tone " s gunners scored hits on " Behar " s prow and stern which killed three of her crew . Five minutes after the sighting , " Behar " s crew and passengers abandoned ship . The steamer sank shortly afterwards and either 104 or 108 survivors were rescued by " Tone " . The " Behar " survivors were maltreated by members of " Tone " s crew . Japanese sailors forced the survivors to hand over all their personal belongings of any value , and then used ropes to tie the survivors in painful positions which caused them to have difficultly breathing . The merchant ship ' s chief officer was beaten after he complained that treating civilians in such a way violated the Geneva Convention . However , the female survivors later had their ropes removed . When the survivors were taken below decks to be imprisoned they were badly beaten by Japanese sailors . Following the attack , Sakonju judged that it was too dangerous to continue the raid as " Behar " s distress message may have alerted the Allies to his force ' s presence . Accordingly , the Japanese turned back for the NEI that day . The heavy cruisers were again escorted through the Sunda Strait by " Kinu " , " Ōi " and five destroyers , and arrived back at the NEI on 15 March . During this time , the " Behar " survivors were held in a small and extremely hot store room on board " Tone " , and were given little access to food and water , sanitary facilities and exercise . Despite Sakonju ' s fears , the Allies were not immediately aware of the attack on " Behar " . Her distress signal had been picked up by only a single Allied merchant ship , which did not report it until she arrived at Fremantle on 17 March . In the meantime , Somerville had decided on 16 March that surface raiders no longer posed a threat to shipping in the Indian Ocean and allowed Allied vessels to resume their normal routing . Massacre . Shortly after the " Behar " survivors were rescued , Sakonju sent a radio message to " Tone " s commanding officer , Captain Haruo Mayuzumi , reprimanding him for taking non - essential personnel prisoner and not capturing the merchant ship . In this message Sakonju ordered that the survivors be killed . Mayuzumi was unwilling to so , however , as he felt that this would violate his Christian religious beliefs . His executive officer , Commander Junsuke Mii , also opposed killing the prisoners . Mayuzumi radioed a request to Sakonju that the prisoners be put ashore , but this was rejected . The captain then visited " Aoba " to argue his case , but Sakonju remained unmoved and told Mayuzumi to " obey my orders " . Despite his misgivings , Mayuzumi decided to kill the prisoners . On 15 March the three heavy cruisers anchored at Tanjung Priok near Java . Following this , either 15 or 36 survivors were transferred to " Aoba " . The party sent to " Aoba " included Symonds , the " Behar " s chief officer and several of the senior officers as well as both of the ship ' s female passengers . All of this group were later landed at Tanjung Priok . The three cruisers sailed from Tanjung Priok bound for Singapore on 18 March . That night , all the prisoners on board " Tone " were beheaded by several of the cruiser ' s officers . Mayuzumi watched the killings from the ship ' s bridge but Mii refused to take part . Aftermath . " Aoba " , " Chikuma " and " Tone " arrived at Singapore on 25 March . The Indian Ocean raid was the last operation conducted by Axis surface raiders during World War II . As a result , " Behar " was the final Allied merchant ship to be sunk by surface raiders during the war . The party of " Behar " survivors who had been landed at Tanjung Priok were initially interred in prisoner of war camps in Java ; the male prisoners were sent to a camp near Batavia and the women were held in a female camp nearby . After all the members of the group had been interrogated , the survivors were separated and sent to other camps in Java or to work as slave labourers in Japan . All the survivors were freed after the end of the war in August 1945 . Following the war , the Allies prosecuted the officers responsible for the murders on board " Tone " . Vice Admiral Takasu had died from disease in September 1944 , but Sakonju was tried by the British in 1947 at Hong Kong and sentenced to death . Mayazumi was also convicted for his role in the killings and sentenced to seven years imprisonment .