'Sa-1' was a Japanese naval sortie against Allied shipping on the route linking Aden and Australia across the Indian Ocean (1/15 March 1944).

The task was entrusted to Rear Admiral Naomasa Sakonju’s 7^th Cruiser Squadron, comprising the heavy cruisers Aoba, Chikuma and Tone.

During February 1944 Admiral Mineichi Koga’s Combined Fleet withdrew from its increasingly vulnerable and isolated main base at Truk atoll in the Caroline islands group, and was divided between Palau and Singapore. The appearance of a powerful Japanese naval force at Singapore concerned the Allies, who feared that these ships might undertake raids in the Indian Ocean and against Western Australia. The Allies therefore strengthened their naval and air forces in the area by transferring two British light cruisers from the Atlantic and Mediterranean, redeploying several US Navy warships from the Pacific, and strengthening their air power in the area of Ceylon and the Bay of Bengal.

Admiral Sir James Somerville, commanding the Eastern Fleet, feared that the Japanese would repeat their devastating 'C' (ii) Indian Ocean raid of March/April 1942, and on 25 February requested permission to withdraw his fleet from its base at Trincomalee in Ceylon so that it was not at risk from the larger Japanese force. The Admiralty directed that the fleet should remain at Trincomalee, unless it was threatened by a superior Japanese force, as its withdrawal would adversely affect local morale and harm British 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.

At a time late in February Vice Admiral Shiro Takasu, commanding the South-Western Area Fleet, ordered the heavy cruisers Aoba, Chikuma and Tone, under the command of Sakonju in Aoba, to raid Allied shipping on the main route between Aden and Fremantle in Western Australia. Takasu directed that if the force captured Allied merchant seamen, all prisoners other than radio operators were to be killed, an order which was not questioned by Sakonju. The Japanese cruisers embarked specialised boarding parties as one of the raid’s objectives was the capture of merchant ships to alleviate Japan’s increasingly acute shortage of shipping.

The Japanese heavy cruisers departed from the Combined Fleet's anchorage in the Lingga Islands on 27 February, and on 1 March the light cruisers Kinu and Oi, supported by five destroyers, escorted the force through the Sunda Strait. The raiders were supported by 10 medium bombers and three or four seaplanes based in Sumatra and western Java, from where they undertook patrols in the direction of Ceylon. Three or four submarines of the 8^th Submarine Flotilla also monitored Allied shipping movements near Ceylon, the Maldive islands group and Chagos archipelago.

Unaware of the Japanese force’s departure, the Allies were nonetheless reinforcing their naval strength in Western Australia after a US ship had encountered Kinu and Oi operating near the Lombok Strait on 6 March. The presence of these ships was taken to indicate that a raiding force had possibly been despatched into the Indian Ocean. On 8 March Somerville directed all Allied ships between 80° and 100° E to divert to the south or west.

After exiting the Sunda Strait, the Japanese heavy cruisers steamed to the south-west for the main route between Aden and Fremantle. The ships were spread 31 miles (50 km) from each other by day, and half this distance by night, and maintained radio silence. On the morning of 9 March they encountered the 6,100-ton British Behar about mid-way between Fremantle and Colombo: the ship was travelling from Fremantle to Bombay as part of a voyage between Newcastle, New South Wales and the UK with a cargo of zinc. Upon sighting the Japanese ships Behar turned away and was shelled by Tone, whose fire hit the freighter’s bow and stern, and also killed three of her crew. The ship’s radio operators managed to broadcast a distress message, however. Five minutes after the sighting Behar's crew and passengers abandoned ship, and the vessel sank shortly after this. Tone rescued 104 survivors. The Japanese cruiser had not tried to capture the freighter as it was judged too risky to sail her back to Japanese territory, and Behar was in fact the last Allied merchant ship sunk by any Axis surface raider.

After the attack, Sakonju judged that it was too dangerous to continue the raid as Behar's distress message might have alerted the Allies to his force’s presence. The Japanese force therefore turned back for the Netherlands East Indies during that day: the three heavy warships were again escorted through the Sunda Strait by Kinu, Oi and five destroyers, and reached Batavia on 15 March.

Despite Sakonju’s fears, the Allies were not immediately aware of the attack on Behar. Her distress signal was picked up by a single Allied merchant ship which raised the alert only when she arrived at Fremantle on 17 March. In the meantime, Somerville 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.

On 16 March Tone disembarked 15 of Behar's survivors, including the ship’s chief officer and two women, at Tanjung Priok. The three cruisers departed for Singapore on 18 March, and during that night the remaining 89 prisoners were murdered on board Tone.

After the war, the Allies prosecuted the officers responsible for the murders: Takasu had died from disease in September 1944, but Sakonju was tried by the British in 1947 at Hong Kong and sentenced to death, and Tone's Captain Haruo Mayazumi was sentenced to seven years in prison.