The 'Battle of Biak' was fought between US and Japanese forces for the island of Biak, and was thus part of the western portion of the New Guinea campaign (27 May/17 August 1944).

Fought on the island of Biak, in Geelvink Bay, as the core of the 'Horlicks' operation, the battle was therefore part of the offensive of General Douglas MacArthur’s South-West Pacific Area command to clear New Guinea of Japanese troops in preparation for an invasion of the Philippine islands group. The battle was the first major Japanese effort to allow uncontested landings and thereby create an inland 'kill zone'. MacArthur’s primary objective was to capture the island so that the Allies could construct airfields. The battle resulted in the capture of the island by Allied forces, which were then used to support operations elsewhere in the Pacific.

Biak is an element of the Schouten islands group, and dominates the entrance to Geelvink Bay, near the western end of New Guinea, The island’s terrain and its location, about 325 miles (523 km) from Hollandia and 180 miles (290 km) from Sarmi, where the Japanese had begun concentrating supply bases and airfields, made it well suited to airfield construction, particularly in its flatter south-eastern area. As the Allies began their advance toward the Philippine islands group in 1944, therefore, MacArthur’s South-West Pacific Area command began planning its capture. in what the planners thought would be an undertaking lasting about one week as there were thought to be only 2,000 Japanese troops holding the area.

Possessing the geographical codename 'Horlicks', Biak is the largest and most northerly of the Schouten islands group, and is technically two islands, the main and larger island of Biak and the smaller Soepiori island on its north-western side. The two are separated by a very narrow stream-like strait called the Sorendidori river, and for this reason Biak is usually considered a single island. Noemfoor island is about 60 miles (100 km) to the west of Biak and Japen about the same distance to the south. Off the island’s south-eastern coast are the Padaido islands, which are 29 forested islets and coral reefs covering an area measuring 21 by 35 miles (34 by 56 km).

Biak measures some 45 miles (72.5 km) on its north-west/south-east axis, and is about 20 miles (32 km) across its centre, which is its widest point, and covers an area of 950 sq miles (2460 km²). Both ends taper to less less than 10 miles (16 km) in width. Soepiori is less than 25 miles (40 km) in length and about 10 miles (16 km) wide at its eastern end. Biak’s surface is covered by a series of very rough terrace-like coral ridges with spur ridges reaching 2,428 ft 740 m) on its north-western end. There are river valleys in the north-eastern end, west central coast, and north-eastern central coast. The highest elevation on Soepiori is 3,392 ft (1034 m). Its mountains lie in clusters and large ridges along the upper south-western coast, down the island’s centre and along the eastern end in an L shape, and on the north-eastern coast. The step-like construction of Biak’s ridges provides some flat areas at different elevations, but they have also been described akin to levees, that is high coral limestone embankments. A cave-pocketed, rugged and narrow coral ridge, up to 250 ft (76 m) high, extends parallel with part of the souther coast. The top of the ridge is wooded, but behind it the broken plateau is covered with scrub brush. Farther island the rising ground is interspersed with patches and bands of forest until about 2 to 3 miles (3.2 to 4.8 km) inland, where the scrub gives way to dense forest. A trail ran behind the ridge parallel with the coast less than 1 mile (1.6 km) inland. The south-eastern interior third of the island has large broken-surfaced flat areas between 150 and 200 ft (46 and 61 m) above sea level. The entire island is covered with dense rain forests and underbrush. The rain is heavy, about 100 in (2540 mm) per year, but there are few streams, other than in the three small river valleys. The rain permeates into the coral, especially on the eastern half of Biak, and is carried away by underground streams into the sea. Rains were to hamper the operation.

Most of the island’s few villages were scattered along the southern coast with Bosnek, the government centre, located on the central part of the south-eastern coast. About 12 miles (19 km) to the west of Bosnek is Sorido, whence a track crosses the island to Korim Bay on the central north-eastern coast. There were no port facilities or protected anchorages, but there were two short jetties at Bosnek and three at Pai in Soenggarai Bay just to the east of Mokmer, itself about midway between Bosnek and Sorido. An area of vertical cliffs backed Parai and called the 'Parai Defile' by US troops. The entire east is fringed by a reef 200 to 600 ft (60 to 185 m) wide. At low tide the reef was dry, but planners possessed no information on the depth of the water at high tide. In many areas there were coral cliffs edging the coast and often, where there were no cliffs, there were mangrove swamps. From east of Bosnek the steep coral ridge closely hugs the coast allowing a strop 400 to 800 yard (365 to 730 m) wide. A road followed this strip on a coral shelf between 10 and 15 ft (3.1 and 13.75 m) high. Small villages, many of whose houses built on stilts over the water, were found there. From Mokmer the ridge turns inland and a gradual but rugged slope rises 1 to 2 miles (1.6 to 2.21 km) from the coast. On this narrow coastal lain, which was covered with scrub brush, the Japanese had built three airfields: from east to west, were Mokmer (the largest), uncompleted Borokoe which the Japanese called Sorido No. 2, and Sorido No. 1 (the smallest). The heaviest Japanese defences had been constructed along this section of the coast where a barrier reef swings out from the fringing reef. At Sorido, the coastal road turns to the north and degenerates into a track headed to the north. A native trail continues along the coast. At Bosnek, the coral ridge backing the village is actually a vertical cliff, and the top of this cliff the Japanese had cleared an airfield but proceeded no further with construction. Two more airfields had also been planned. Intended for use by the 23d Air Flotilla, their utility ceased en Allied aircraft began operating from Hollandia.

The Japanese forces on Biak were designated the Biak Detachment and were centred on the 222^nd Regiment of the 36^th Division under the command of Colonel Naoyuki Kuzume. To this infantry core were attached anti-aircraft, airfield construction, transport and service units plus the 19^th Naval Garrison Force and naval anti-aircraft units. The Biak Detachment totalled 12,000 men and was to have been reinforced by the 221^st Regiment of the 35^th Division at Halmahera to the west. The Allied estimate of the Japanese strength was 4,400 men, of whom about half were rated as combat troops. The Japanese converted service units into combat units as the invasion fleet approached. The defences were concentrated on the southern coast above the ridge extending from Soriari westward to Soenggarai Bay. Where the coast bends at Mokmer and the ridge turns inland there was a gap in the defence. Heavy defences were located on the inland ridge overlooking Mokmer airfield, and artillery was hidden in cave positions.

Owi island, one of the largest islands of the Padodo island group, and the closest to Biak, is 2.5 miles (4 km) to the south-east of Mokmer and defines Soenggarai Bay. It measures about 3 miles (4.8 km) on its north-east/south-west axis and is 1.5 miles (2.4 km) wide. It is mostly flat, but there are two narrow parallel ridges more than 100 ft (30 m) high extending along most of its length. Most of the island is covered with scrub brush, but a wooded band follows the north-western coast and bends around the south-western end.

The landing site selected for 'Horlicks' was at Bosnek with its two jetties and located near the eastern end of the Japanese defences. Major General Horace H. Fuller’s 41^st Division (162^nd, 186^th and 163^rd Infantry at Wakde and Sarmi, with significant support units attached, constituted the 'Hurricane' Task Force, whose land forces were to be landed by the 2^nd Engineer Special Brigade. The 128^th Infantry of the 32^nd Division, and the separate 158^th Infantry were designated the 'Alamo' Force Reserve, for both Biak and the 'Straightline' assault on Wakde-Sarmi. Z-Day was set for 27 May, 10 days after the beginning of the Wakde-Sarmi landing. The 'Hurricane' Task Force undertook a scalled-down rehearsal at Humboldt Bay and departed for Biak on 25 May on board the ships of the Western Attack Group. US, Australian and Dutch aircraft had been heavily involved in 'softening' the area.

The four landing beaches were Beaches Green 1, 2, 3 and 4. Allied planners considered these beaches to be poorer for landing operations than those farther away from the airfields, but they were nonetheless selected for their proximity to the main Allied objectives and because air reconnaissance indicated that the beaches were not backed by cliffs or swamps, and that there were two jetties nearby that might facilitate deep-water port access.

Commanded by Rear Admiral William M. Fechteler under the overall command of Rear Admiral Daniel E. Barbey’s VII Amphibious force, the Task Group 77.2 transport and assault force comprised five destroyer transports, eight LSTs, eight LCTs, and 15 LCIs supported by a myriad of smaller vessels including DUKWs, LCVPs and LVTs, which were chosen in reflection of concerns about the coral reef opposite the landing beaches. The assault transport and landing force was protected by two heavy cruisers, three light cruisers, and 21 destroyers including several Australian vessels including the cruisers Australia and Shropshire and the destroyer Warramunga. Close air support for the operation was provided by Lieutenant General George C. Kenney’s US 5^th Army Air Force operating from Hollandia and Wakde island, although elements of US 13^th Army Air Force, as well as Australian and Dutch squadrons operating from bases as far distant as Darwin, also provided strategic air support.

As noted above, Allied intelligence greatly underestimated the number of Japanese troops holding the island, which was in fact held by 11,400 men under the command of Colonel Naoyuki Kuzume. Initially, the majority of the combat troops, totaling about 4,000 men, were drawn from the veteran 222^nd Regiment of the 36^th Division, which had previously served in China, together with a small armoured element and supported by artillery, anti-aircraft, construction and naval guard and base troops, the last two totalling 1,500 men under the command of Rear Admiral Sadatoshi Senda. These troops were reinforced by elements of the 35^th Division's 219^th Regiment and 221^st Regiment.

Given the length of coast he saw as vulnerable to amphibious assault, together with the new Japanese doctrine of ibland defence and his appreciation of the Allied objectives, Kuzume focused his defensive plans away from the water’s edge. Instead, he decided to carry out a feint, allowing the US forces to come ashore unopposed so that they would advance into the trap he had prepared for them on the basis of complex of caves to the west of Mokmer and to the east of Bosnek. This defensive complex was intended to turn the area around the vital airfield into a honeycomb of defended caves and pillboxes filled with infantry, automatic weapons, artillery, mortar batteries and a single company of Type 95 Ha-Go light tanks. The western caves were interconnected by a series of underground tunnels and had been constructed largely for fighting purposes. Kuzume also stockpiled these positions with ammunition and other supplies, with several dumps located around the eastern cave area, along with living quarters for the defenders. Water was limited on Biak and had to be strictly rationed by the US troops, and heat and humidity would take a heavy toll during the fighting.

The Allies knew from an intercepted message of 5 May that the the intelligence branch of General Korechika Anami’s 2^nd Area Army, responsible for the defence of the Philippine islands group and western New Guinea, thought the next Allied landing would probably be on Biak, and a preliminary landing was made on 17 May at Wakde on the way to Biak. There a smaller airfield was available, which could be used as an advanced base until the Biak airstrips were ready. While initial Allied intelligence estimates of Japanese troops suggested the presence of about 5,000 men, an intercepted message at the end of April gave the ration strength as 10,800, though it was thought this was a figure based on projected rather than current strength.

The transport and landing force assembled largely in the Humboldt Bay area near Hollandia, and after only limited rehearsals departed at a time late on 25 May. After a 45-minute pre-landing naval bombardment, Major General Horace H. Fuller’s 41^st Division (162^nd ,163^rd and 186^th Infantry) started to come ashore on Biak on 27 May 1944, initially with the 162^nd Infantry soon followed by the remainder of the division, including the 163^rd and 186^th Infantry. By 17.15 some 12,000 men had landed, together with 12 M4 Sherman medium tanks, 29 field guns, 500 vehicles and 3,000 tons of supplies, including 600 tons aboard vehicles. Several minor Japanese air attacks took place against the US beach-head on this first day: at first these were not pressed heavily, but in the afternoon two waves of aircraft attacked the LSTs around the western jetty. Several bombs were dropped, but these failed to detonate. Three aircraft were destroyed and one was badly damaged by anti-aircraft fire from the US ships and guns which had been brought ashore.

After a brief attack on the beach-head by a group of Japanese light tanks, which was defeated by a group of Sherman tanks in the first tank-versus-tank engagement of the Pacific War, the US regiment moved inland quietly confident and expecting little opposition, a perception that was rudely changed when the regiment reached the airfield. From low-lying terrain and surrounding ridges came a storm of heavy weapons fire that pinned down the US troops. It was not until dark that amphibious tractors could be brought up to extricate the infantry from the trap. On the following day the regiment reached the end of Mokmer airstrip. The Japanese held firm, delaying its capture. Given the slow progress, the US command pulled their forces back, relieved Fuller of command and reinforced the division with the 34^th Regimental Combat Team of Major General Frederick A. Irving’s 24^th Division.

On 5 June the 186^th Infantry, with the 2/162^nd Infantry attached, moved to the eastern bases of the ridges dominating Mokmer airstrip. A co-ordinated attack on 7 June resulted in the capture of Mokmer airstrip and the establishment of a beach-head to the south of the strip. Japanese resistance continued in the area, however, particularly in the caves overlooking the area, and this prevented engineers from improving the airstrip. The engineers resumed their efforts on 13 June, but were once again disrupted by the Japanese. Lieutenant General Robert L. Eichelberger, commander of the US I Corps, assumed command of the 'Hurricane' Task Force on 15 June, tasked with renewing the attack. The new attack plan was to drive the Japanese from all the terrain from which they could fire on the Mokmer airstrip. First the West Caves, the Japanese encampment area, was cleared by the 186^th Infantry, which then moved on the ridges. The 34^th Regimental Combat Team, supported by the 167^th Field Artillery Battalion, occupied Borokoe and Sorido airstrops almost without opposition.

The US forces had been delayed by 10 days. With the delay, the 5^th Army Air Force’s command looked for alternative sites from which the air force could operate and arranged the capture of the nearby Owi island on 2 June: here Owi airfield was constructed, this comprising two 7,000-ft (2135-m) runways. An advanced echelon stationed there comprised a bombardment group, two fighter groups, a Northrop P-61 Black Widow twin-engined night-fighter group, and a garrison of 15,000 troops.

The battle for control of Biak nearly became a critical turning point in the campaign for the Pacific. The Imperial Japanese navy had long been seeking to engage the US Navy in a decisive battle, the Kantai Kessen, that would enable them to win the war. Biak was not far from major Japanese fleet units and there were a number of land airfields nearby that could support the land-based aircraft the Japanese were hoping to concentrate to defeat the US fleet. The Imperial Japanese navy’s chief-of-staff, Vice Admiral Ryunosuke Kusaka, believed that Biak represented the Allies' main effort, and a counterattack at Biak could provoke the US Navy into engaging in a major action. In response to the landing at Biak by US forces, therefore, the Japanese launched an operation to reinforce the area. For air support, the Japanese 23^rd Kokutai (air flotilla) initially had only 18 aircraft but was later reinforced with as many as 166 aircraft, which were moved to Sorong, in Dutch New Guinea from Japan and the Mariana islands group.

The Imperial Japanese navy also began planning to reinforce the island in 'Kon', planning for which began on 29 May. A total of 2,500 troops from the 2^nd Amphibious Brigade were assigned for transport from Mindanao in the Philippine islands group under escort of a force under the command of Rear Admiral Naomasa Sakonju. This force comprised the battleship Fuso, the heavy cruisers Aoba, Myoko and Haguro, the light cruiser Kinu and eight destroyers (five as part of the screen and three as part of the transport element). They were scheduled to reach Biak on 3 June, and other reinforcements were to be transported from Manokwari by barge.

Admiral Teijiro Toyoda, commander of the Combined Fleet, initially attempted to reinforce Biak to ensure that the airstips were held, but his first reinforcement, despatched on 1 June, turned back after a Japanese scouting aeroplane mistakenly reported a US aircraft carrier in the vicinity. A second relief effort on 8 June was intercepted and driven off by US and Australian naval forces. A third attempt, with the support of the super-battleships Yamato and Musashi, was scheduled for 13 June, but the US 'Forager' invasion of the Mariana islands group forced the Japanese to redirect their forces toward the Mariana islands group for the 'A' major confrontation in the 'Battle of the Philippine Sea'.

These naval efforts were coupled with heavy air attacks. On 2 June, in support of the Japanese reinforcement effort, there was a heavy air attack on the US LST forces around Biak: 12 out of 54 attacking aircraft were lost, while one Allied LST suffered a near miss. On the following day, another major air attack was undertaken by Japanese aircraft against Allied vessels around Biak, resulting in minor damage and the loss of 11 out of 41 aircraft. In total, three reinforcement efforts were undertaken as part of 'Kon', as well as further barge operations: several large vessels and a number of aircraft were lost by the Japanese during these efforts, although about 1,200 men of the 219^th, 221^st and 222^nd Regiments were landed during June.

The RAAF’s No. 1 Wireless Unit, an Australian radio intercept and monitoring unit, learned that at the time of the invasion Lieutenant General Takuzo Numata, the 2^nd Area Army's chief-of-staff, was on the island for an inspection tour. Numata sent messages requesting his evacuation, and a floatplane was sent in from Korim Bay on the night of 20 June to extract him. After two more days of intense fighting, Kuzume burned the regimental colours, indicating to his men that the regiment would make the defence of Biak their final battle, and then committed suicide, showing his men he did not fear death.

Allied engineers resumed their work on Mokmer airfield on 20 June. The US forces broke through the Japanese defences on 22 June, capturing the coastal strip from Bosnek to Sorido, including the three airfields at Sorido with its 4,500-ft (1370-m) runway, Borokoe with its 4,500-ft (1370-m) runway and Mokmer with its 8,000-ft (2440-m) runway. About 3,000 Japanese remnants tried to organise a final counterattack up to 17 August.

The capture of Biak island cost the Allied ground forces 438 men killed and 2,361 wounded or injured in action, while casualties among naval forces amounted to 22 men killed, 14 missing and 68 wounded. In addition, US forces suffered 7,234 non-battle casualties, the majority of these being victims of scrub typhus. About 600 British Indian and Javanese forced labourers were released from Japanese custody after the battle. The Japanese had fought to annihilation, with 4,700 men killed and only 200 surviving to be taken prisoner, while the remainder faced death from disease and starvation in the following months. The Japanese tactics of allowing the landing and delaying their firing until there were a great many targets were repeated at other battles, including the 'Battle of Peleliu' and 'Battle of Okinawa' in 'Stalemate II' and 'Iceberg' respectively.

The Allies subsequently developed Biak into a logistics base and constructed several airfields in the area. Several runways were constructed by US engineers on nearby Owi, while Mokmer airfield was declared operational on 22 June, and was further improved and expanded with hardstandings for more than 100 aircraft throughout July and into August. Other airfields were constructed at Borokoe and Sorido, although the latter airfield was not completed for lack of manpower and unsuitable terrain. These airfields were not completed in time for use during operations to capture the Mariana islands group in June, however, but were utilised during follow-on actions against the Palau islands group in September. Biak was also used to strike targets on Mindanao and in the Netherlands East Indies. The port facilities around Biak were also improved, with eight berths constructed for LSTs along the southern coast, while two floating docks were constructed at Bioak and Owi to facilitate use by 'Liberty' ships. Several other docks and jetties were constructed or improved, while several roads (12 miles/19 km on Owi and 30 miles/48 km on Biak) were constructed around the island to improve internal lines of communication; another 22 miles (35 km) of existing roads on Biak were also improved. A 400-bed hospital was also constructed, while another was planned but ultimately not completed.