'Boomerang' (ii) was a US air attack by the XX Bomber Command of General Henry H. Arnold’s 20^th AAF from a forward base near Trincomalee in Ceylon against the Japanese-operated oilfields and their associated installations near Palembang at the south-eastern end of Sumatra in the Japanese-occupied Netherlands East Indies (10/11 August 1944).

The raid involved attempts to bomb an oil refinery at Palembang in the southern part of Sumatra and to lay mines to interdict the movement of traffic up and down the Musi river. As such, the raid constituted part of a series of attacks on Japanese-occupied cities in South-East Asia that Brigadier General LaVerne G. Saunders’s XX Bomber Command undertook as an adjunct to its primary mission of bombing Japan, and indeed on he same night as 'Boomerang' (ii) aircraft of the command raided the Japanese city of Nagasaki.

Some 54 Boeing B-29 Superfortress four-engined heavy bombers were dispatched from an airfield on the British colony of Ceylon on 10 August, and of this total 39 reached the Palembang area. Attempts to bomb the oil refinery were largely unsuccessful, only a single building being confirmed as having been destroyed. Mines dropped in the river connecting Palembang to the sea sank three ships and damaged four others. British air and naval forces provided search-and-rescue support for the US bombers. The Japanese anti-aircraft guns and fighters entrusted with the defence of Palembang failed to destroy any of the US bombers, but one B-29 ditched when it ran out of fuel. This was the only USAAF raid on the strategically important oil facilities at Palembang, and these were also attacked by aircraft operating from British aircraft carriers in January 1945.

After its 'L' conquest of the island during February and March 1942, the Imperial Japanese army controlled the Royal Dutch Shell company’s oil refineries on Sumatra, these including Pangkalan Brandan and Pladjoe (Pladju), as well as the Standard-Vacuum Oil Company (Stanvac) refinery at Sungei (Soengai) Gerong. The oil refined at the small Pangkalan Brandan refinery in northern Sumatra was transported to port facilities at nearby Pangkalan Susu for shipment directly to Singapore and other locations in the Malayan area.

Oil production was centred at Prabumulih, some 43.5 miles (70 km) from Palembang in the south-eastern part of Sumatra. From this crude oil was piped to the large Pladjoe refinery, a few miles to the north of Palembang. It was in February 1942 that the Japanese 2^nd Parachute Regiment captured Pladjoe before it could be destroyed, and the Japanese later named Pladjoe, which was managed by Nihon Sekiyu, as the 'No. 1 Refinery'. This facility was able to refine 45,000 barrels per day and its speciality was high-octane aviation fuel production. In the period before World War II, Stanvac also operated several oilfields and transported the crude oil to its Sungei Gerong refinery, to the east of Palembang. After they had captured Sungei Gerong, they named it the 'No. 2 Refinery', and under the management of Mitsubishi Sekiyu this too was capable of refining 45, 000 barrels per day. These two refineries, which were the largest in South-East Asia, had a combined annual capacity of 20.46 million barrels, and were capable of producing 78% of Japan’s aviation fuel and 22% of its fuel oil requirements.

The Imperial Japanese army used captured British and Dutch tankers, most of them comparatively small, to transport fuel across the Musi (Moesi) river, which joins the Ogan and Komering rivers near Palembang. Below Palembang, the Musi is deep enough for ocean-going vessels and about 50 miles (80 km) to the north it enters the waters of the Bangka Strait. Japan’s wartime demands for fuel were so great that almost daily trips were needed to transport the oil from Sumatra to Singapore for further shipment to other parts of the Japanese empire. Fuel also was transported either in bulk or by case (tins) to the smaller more remote locations in and around Malaya and the former Dutch East Indies.

Asiatic Petroleum, a subsidiary of Royal Dutch Shell Oil, formerly owned storage facilities at Pulau Bukum and Pulau Sebarok near Singapore, and petroleum products were delivered by sea from Sumatra and stored in these captured centres. Round trips from Palembang to Singapore and back, including loading and discharging fuel, averaged about one week, but many trips took longer, indicating possible loading and unloading difficulties and/or the ships' engine problems and perhaps groundings.

Their very remoteness in Sumatra permitted the operation these oil facilities by the Japanese with impunity from Allied attack until the Allied meeting at the 'Sextant' conference at Cairo in Egypt during November 1943. Attended by President Franklin D. Roosevelt, Prime Minister Winston Churchill, Generalissimo Chiang Kai-shek and the British and US Combined Chiefs-of-Staff, the conference was intended to address future military operations against Japan, and one of the agreements reached was for the bombing of vital targets in the Dutch East Indies during 1944.

It was at a time late in 1943 that the US Joint Chiefs-of-Staff had approved a proposal to begin the strategic air campaign against the Japanese home islands and Japanese targets in East Asia by basing B-29 heavy bombers in India and establishing forward airfields in China. The main element of this strategy, designated 'Matterhorn', was to construct airstrips near Chengdu in inland China which would be used to refuel B-29 bombers staging from bases in the Bengal area of north-eastern India en route to targets in Japan. The implementation of 'Matterhorn' was entrusted to the 20^th Army Air Force’s XX Bomber Command. The head of the USAAF, General Henry H. Arnold, exercised direct command of the 20^th AAF as he had established it as an independent strategic force which reported to the Joint Chiefs-of-Staff rather than the combat theatre commanders in the Pacific, namely Admiral Chester W. Nimitz of the Pacific Ocean Areas and General Douglas MacArthur of the South-West Pacific Area. Brigadier General Kenneth B. Wolfe initially led the XX Bomber Command, which undertook its first combat mission, against Bangkok in Thailand, on 5 June. During this operation, two B-29 bombers ran out of fuel over the Bay of Bengal during their return flights to India and were forced to ditch.

The decision to attack Palembang, in the period preceding the approval of 'Matterhorn' resulted from debates concerning how best to exploit the capabilities of the B-29 force. Late in 1943 and early in 1944, serious consideration was given to initial employment of the B-29 force to attack merchant shipping and oil facilities in South-East Asia from bases in northern Australia and New Guinea. The final plan for 'Matterhorn', approved by the Joint Chiefs-of-Staff in the course of April, specified that while the XX Bomber Command would focus on Japan, it was to also attack Palembang. These raids were to be staged through airfields in Ceylon. The inclusion of Palembang in the plan represented a compromise between the strategists who wanted to concentrate the force exclusively against Japan and those who wished to focus it on oil targets. For planning purposes, the date for the first attack on Palembang was set at 20 July 1944.

Infrastructure development was undertaken in Ceylon to support the planned raids on Palembang. In March 1944, work began to modify four airfields on Ceylon to the standard required for B-29 operations, the British airfields at China Bay and Minneriya being accorded the highest priority. These two airfields were scheduled to be ready by July. In April, when it became apparent that both could not be completed in time, it was decided to concentrate on China Bay. This airfield was capable of accommodating 56 B-29 bombers of the 58^th (Very Heavy) Bombardment Wing by the middle of July and was fully operational by the time 'Boomerang' (ii) was flown.

Shortly after XX Bomber Command’s first attack on Japan, made against Yawata on the night of 15/16 June, Arnold pressed Wolfe to attack Palembang as part of the follow-up raids. In his reply, Wolfe noted that it would not be possible to do so until 15 July, when it was expected that the airfield at China Bay world be ready. On 27 June, Arnold issued the XX Bomber Command with a new targeting, which specified that 50 B-29 bombers be despatched against Palembang as soon as the airfield was complete. Wolfe was transferred to a role in the USA on 4 July, and three days later Saunders assumed command on a temporary basis. Saunders decided to delay the attack on Palembang until the middle of August to enable the XX Bomber Command first to make a maximum-effort raid on Anshan in China, which Arnold had accorded the highest priority.

Planning for the attack on Palembang had begun in May. As a result of the very long distance which was to be flown and the need to stage through Ceylon, the operation required more planning and preparations than any of the other raids conducted by the XX Bomber Command. USAAF and RAF personnel worked together to complete the preparations. The British supplied fuel for the operation and met the cost of upgrading the Ceylon airfields under reverse Lend-Lease arrangements. Including its accommodation facilities and transport vehicles, China Bay was virtually given over to the USAAF.

The plan for the operation evolved over time. The 20^th AAF initially ordered that the attack involve all 112 of the XX Bomber Command’s aircraft, and be undertaken by day. The command sought to have this directive modified on the grounds that the launch of so many aircraft from a single airfield would mean that the force would have to be divided into several waves. Splitting the force in this way would further complicate the operation, and was considered likely to lead to higher losses. Arnold accepted this argument, and the 27 June targeting directive specified that the attack take place either at dawn or dusk. The meteorologist assigned to the operation recommended that the attack be made at night so that the B-29 bombers could take advantage of favourable tailwinds, and the XX Bomber Command gained the 20^th AAF’s agreement to this change.

During the period in which the plan was prepared, several US intelligence agencies altered their views regarding the importance of Palembang. The USAAF’s Assistant Chief of the Air Staff, Intelligence, and the Committee of Operations Analysts judged that the changing tactical situation in the Pacific theatre and the heavy losses of Japanese shipping meant that the Pladjoe refinery was no longer of critical importance to the Japanese war effort. The XX Bomber Command staff wanted to cancel the undertaking, which it saw as a distraction from the main effort against the Japanese steel industry. The Joint Chiefs-of-Staff continued to require that Palembang be attacked, and Arnold included it in another target directive issued in July. After it was confirmed that the facilities at China Bay would be ready by 4 August, Arnold directed that the raid be made by 15 August.

Several targets were specified. The primary target was the Pladjoe refinery and the secondary target the nearby Pangkalan refinery. The Indarung cement factory at Padang was the last-resort target for aircraft unable to reach Palembang. Part of the force was tasked with dropping naval mines to interdict the Musi river, along which all the oil produced at Palembang was shipped. As a result of the extreme range from Ceylon to the targets and back (3,855 miles; 6205 km to Palembang and 4,030 miles; 6490 km to where mines were to be dropped), each of the bombers was to carry only 2,000 lb (907 kg) of bombs or mines, and to have their fuel tanks filled to capacity. Planning for the attack was completed on 1 August.

An attack by XX Bomber Command on the Japanese city of Nagasaki was scheduled to take place on the same night as the raid on Palembang. The USAAF official history states that it was hoped that attacking two targets 3,000 miles (4830 km) apart from each other would have a psychological impact on the Japanese.

The defence of the oilfields and oil facilities on Sumatra against air attack was the responsibility of the Imperial Japanese army. The Palembang Air Defence Headquarters had been created in March 1943 for this purpose, and initially comprised the 101^st Air-Defence Regiment, 102^nd Air-Defence Regiment and 103^rd Air-Defence Regiment together with the 101^st Machine Cannon Battalion. Each of the air-defence regiments was equipped with 20 75-mm (2.95-in) Type 88 anti-aircraft guns, and may also have included a cannon battery and a searchlight battery. In January 1944, Lieutenant General Ryuichi Torita’s 9^th Air Division was established as part of efforts to strengthen Sumatra’s air defences. The Palembang Air-Defence Headquarters had been redesignated as the Palembang Defence Unit and was assigned to the 9^th Air Division upon that command’s formation. At around this time, the unit was expanded to include fighter aircraft. The 21^st Fighter Regiment and 22^nd Fighter Regiment of the Imperial Japanese army air force were responsible for the interception of Allied aircraft. The 101^st, 102^nd and 103^rd Air-Defence Regiments and the 101^st Machine Cannon Battalion remained, and had been supplemented by the 101^st Anti-Aircraft Balloon Regiment, which operated barrage balloons.

On the afternoon of 9 August, 56 B-29 bombers of the 444^th and 468^th Bombardment Groups arrived at China Bay from Bengal. The attack force began to take off from China Bay at 16.45 on 10 August. A total of 54 B-29 bombers was despatched. One of the aircraft returned to the base 40 minutes after taking off as a result of engine problems, but it had been repaired within two hours, and took off again bound for Sumatra.

The bombers' journey to Sumatra was uneventful. The aircraft flew individually on a direct course from China Bay to Siberoet island off the west coast of Sumatra. After reaching Siberoet, the bombers changed course to the Palembang area. Several British warships of the Eastern Fleet and a number of RAF aircraft were positioned along this route to rescue the crews of any US bombers which had to ditch. Royal Navy vessels involved included the light cruiser Ceylon, the destroyer Redoubt and the submarines Terrapin and Trenchant. The submarines also served as navigation beacons.

Thus it was within this context that on the night of 10/11 August 1944 the USAAF undertook 'Boomerang' (ii). The bombers lifted off from their base at Chengtu in China, staged through the newly completed 7,200-ft (2195-m) runway at China Bay to make a radar-guided night attack on the Pladjoe refinery. The bombers flew individually from China Bay straight to Siberoet island, off Pandang in southern Sumatra, and then directly to Palembang. About 12 of the bombers failed to attack for varied reasons, but 39 aircraft reached their primary targets, two bombed the secondary target of Pangkalan Brandan refinery, one bombed the airfield at Djambi and eight mined the Musi river along which all of Palembang’s product was shipped. Just nine aircraft of Colonel Alva D. Harvey’s 444^th Bomb Group reached Palembang and attacked through heavy overcast with 36 500-lb (227-kg) HE bombs and 16 photo-flash bombs. Descending 500 ft (150 m) below the 1,000-ft (305-m) ceiling, the bombers strafed Japanese ships on the Musi river and dropped 16 mines in the first such operation by the B-29. The aircraft claimed three ships sunk, two others damaged and a one-month closure of the river approach to the refinery.

The results at Pladjoe were unobserved, but later deemed poor, and as a result no other B-29 raids were staged through Ceylon.

The 3,855-mile (6205-km) flight of 19 hours 40 minutes from Ceylon to Palembang and the parallel 4,030-mile (6485-km) flight to the Musi river and back, were the longest single-stage missions flown by USAAF combat aircraft in World War II.

A total of 31 B-29 aircraft attempted to bomb the Pladjoe refinery. It proved difficult for their crews to locate the target, as no lights were showing in Palembang, patchy cloud covered the area and the bomber which had been tasked with illuminating the refinery with flares did not reach the area. Instead, the bombardiers aimed on the basis of radar or visual sightings through breaks in the clouds. The US airmen reported seeing some explosions and fires, but the attack photographs taken from the bombers were indistinct. Eight B-29 bombers descended below the clouds to drop two mines each into the Musi river, and the accuracy of this attack was assessed as 'excellent' in a post-attack report. As noted above, this was the first occasion in which the B-29 had been used as a minelayer.

Of the 15 B-29 bombers which failed to reach the Palembang area, three attacked other targets. Two aircraft bombed the oil town of Pangkalanbrandan in the northern part of Sumatra and the third struck an airfield near the town of Djambi. Several of the bombers which had to turn back did so after running short of fuel.

The Japanese attacked the B-29 bombers while they were in the Palembang area, but without success. Anti-aircraft guns and rockets were fired, and the US crews sighted 37 Japanese aircraft. Some of the fighters pursued the bombers for 350 miles (565 km), but managed to damage none of the B-29 aircraft.

One B-29 ditched into the sea 90 miles (145 km) from China Bay on its return flight after running out of fuel. Its crew were able to send an SOS signal before ditching, which led Allied forces to conduct an intensive search of the area. One of the bomber’s gunners was killed, and the other members of the crew were rescued on the morning of 12 August. While the Allied planners had expected that several B-29 bombers would have to ditch as a result of fuel shortages, this proved to be the operation’s only loss. The mission lasted about 19 hours, and the mining of the Musi river is considered the longest combat mission of the war.

The attack on Nagasaki on the night of 10/11 August in conjunction with 'Boomerang' (ii) was unsuccessful. The city was bombed by 24 B-29 aircraft, but little damage was inflicted. Two other bombers turned back after departing the forward airfields in China, and three attacked secondary targets. All of the US aircraft returned to base.

'Boomerang' (ii) therefore yielded mixed results. Photographs of the Pladjoe refinery taken on 19 September indicated that a single building had definitely been destroyed in the raid, though several others were assessed as 'probables'. The minelaying element of the attack was successful: three ships totalling 1,768 tons were sunk, four others were damaged and the Japanese were unable to transport oil via the Musi river for one month before minesweeping had been completed. B-29 bombers later laid very large number of mines as part of efforts to blockade Japan. Despite the failure of 'Boomerang' to achieve its goals, it demonstrated that the XX Bomber Command was now capable of conducting complex operations and the B-29 bombers could make safe long-distance flights over water.

The XX Bomber Command continued to be reluctant to attack Palembang, and recommended to the 20^th AAF on 24 August that its facilities at China Bay be abandoned. Approval to do so was granted on 3 October, though the 20^th AAF ordered that the aircraft fuelling system remain in place. No other B-29 attacks were conducted through Ceylon. The XX Bomber Command attacked several other cities in South-East Asia during 1944 and in the early part of 1945: these included several raids on Singapore in Japanese-occupied Malaya, and these required even longer flights than those to reach Palembang.

The Eastern Fleet’s aircraft carriers raided oil facilities in Sumatra several times between November 1944 and January 1945. These included two attacks on Palembang as 'Meridian' in January 1945. On 24 January the fleet’s aircraft badly damaged the Pladjoe refinery, and on 29 January serious damage was inflicted on the nearby Sungai Gerong refinery. The Japanese general who commanded the oil refineries at Palembang stated after the war that these attacks had inflicted much more damage than 'Boomerang' (ii).

On 28 August, the XX Bomber Command, now commanded by Major General Curtis E. LeMay, operated against the waters off Penang, Singapore, Saigon, Cam Ranh Bay, Pakchan and the estuary of the Yangtze river.

In conjunction with the long-distance raid on Palembang and to maximise psychological impact of long-range bombing on Japan’s leaders, on the same night other aircraft of the 444^th Bomb Group flew a 3,120-mile (5020-km) raid on the Japanese port city of Nagasaki, which the aircraft bombed from an altitude of 18,000 ft (5485 m). Seven of the bombers are credited with hitting their primary target.

On 5 November 1944 the XX Bomber Command launched 76 B-29 bombers from Kharagpur, to the west of the Indian city of Calcutta, on the first USAAF attack on Singapore. Each of the aircraft was armed with just two 1,000-lb (454-kg) bombs as a result of the great distance to Singapore. The primary target was the former British 'King George VI' graving dock and the secondary target was the refinery at Pangkalan Brandan. Some 53 of the bombers attacked Singapore and seven attacked Pangkalan Brandan.