The battle of Biak Island (27 May- 29 July 1944) was one of the most costly of MacArthur's leapfrogging attacks on the north coast of New Guinea and saw a well dug-in Japanese garrison hold out for several months longer than originally expected.
Biak Island was a very strong defensive position. Although it was a coral island, it wasn't flat like most of the coral atolls, but instead contained high cliffs, hills and countless massive caves. The southern coast was protected by coral reefs and lined by 250ft high cliffs. The biggest area of flat ground was towards the southern tip of the island, and the Japanese had built three airfields here (Mokmer airfield in the east, Borokeo airfield in the centre and Sorido airfield in the west). In addition the Americans had badly underestimated the strength of the Japanese garrison and believed that there were between 2,000 and 4,000 men on the island.
The island was garrisoned by 11,000 men under Colonel Naoyuki Kuzume. As had been the case at Hollandia and Aitape, most of these men were support staff, and only about a third of them were front line troops but unlike at Hollandia Kuzume had prepared an excellent defensive plan. He decided to defend the three airfields on the southern side of the island by digging in to the hills above them. A network of supply dumps, machine gun and howitzer emplacements and other strongpoints were built into the caves, allowing the Japanese to dominate the landing beaches. The caves would also prove to be largely immune to the pre-invasion naval and air bombardments, and very difficult to knock out with conventional weapons. When the battle began General Takazo Numata, Chief of Staff of the 2nd Area Army, was in the island for an inspection visit, and he took command of the Japanese efforts.
The attack was to be carried out by all but one regiments of the 41st Division (General Horace Fuller). The other regiment from the division was allocated to the invasion of the Wakde-Sarmi area, which was timetabled to begin ten days earlier in order to allow the same assault vessels to be used for both attacks.
The plan was to land on the south coast east of the Japanese airfields. The pre-invasion bombardment did cause a haze that obscured the coast, and when the 41st landed on 27 May it found itself 3,000 yards to the west of the original landing beach, facing a mangrove swamp. As the Japanese had decided not to try and defend the beaches the landing was unopposed, and the beachhead was firmly established by the end of the 27th.
The battle turned into something of an embarrassment for MacArthur. On 28 May he issued a communiqué announcing the imminent end of the campaign. On 1 June he announced that enemy resistance was 'collapsing' and on 3 June talked about 'mopping up' operations. These announcements came at the very start of a battle that didn’t officially end until late August.
Immediately after landing the 162nd Regiment began to advance west towards the airfields. This mean that the American beachhead was long but narrow, and on 28-29 May the Japanese counterattacked and cut the coastal road between the 162nd and the beachhead. The isolated regiment had to be rescued by ship and returned to the main beachhead.
On 31 May the 41st Division's third regiment, the 163rd, landed on Biak after being withdrawn from the Wakde-Sarmi battle. Once these reinforcements arrived the Americans began to prepare for a second offensive. This time General Fuller decided on a two-pronged attack, with the 162nd advancing along the coast and the 186th on a parallel route inland. The attack began early on 1 June, and made steady progress. On the night of 1-2 June the Japanese attacked the 3rd Battalion, 186th Infantry. The attack was repulsed with heavy losses - at least 86 dead including the commander of the 1st Battalion, 222nd Infantry. The Americans lost 3 dead and 8 wounded. The advance resumed early on 2 June. During the day the Americans realised that they were advancing into one of the main Japanese strongpoint, an area known as the Ibdi Pocket. The main effort for the next days went into clearing this pocket. 4 June was a quiet day as the Americans waited for a possible Japanese counterattack after aerial reconnaissance suggested reinforcements were heading to Biak. This attack didn't materialise and the attack resumed on 5 June.
On 6 June the 186th was about to begin an attack on the high ground north of Mokmer Airfield, when new orders reached the battalion from General Fuller. He wanted the airfield to be taken as quickly as possible and ordered the battalion to leave the ridges and attack the airfield and a beach to the south. The battalion commander objected, but Fuller was under pressure from above.
The attack on Mokmer Airfield was launched early on the morning of 7 June. The airfield fell very quickly, but the Americans had now moved into the exact position that the Japanese wanted. At 9.45am a ring of Japanese guns opened fire from the surrounding ridges, marking the start of a four hour bombardment. The Americans held out, and by the end of the day had secured the position on the airfield, but with the ridges still in Japanese hands they were no nearer to being able to bring it into use. The Americans made little progress over the next four days, but they did manage to get the 162nd Infantry to Mokmer airfield to reinforce the 186th.
A new attempt to clear the area north of the Mokmer airfield began on 11 June. On 11 June the 162nd and 186th advanced west from their bridgehead and secured most of the airfield. On 12 June the began to push north, and on 14 June they secured most of the lower lying land north of the airfield. By the end of 15 June the Japanese had been pushed back into a small defensive area north-west of the airfield, close to one of their major defensive positions known as the West Caves.
By now the American high command was frustrating with what they saw as the unacceptably slow progress on Biak. The decision was made to place General Eichelberger, commander of I Corps, in command of the expeditionary force, replacing General Fuller, who was to be left in command of his division. Eichelberger arrived on 15 June and Fuller made it clear that he wasn’t willing to remain on the island under those circumstances. General Fuller was relieved on 18 June, but as a sign of the high regard he was still held in was made Deputy Chief of Staff for Admiral Mountbatten's Southeast Asia Command. General Doe, deputy commander of the 41st Division, took over as divisional commander.
As was so often the case during the Second World War the new commander took several days to examine the situation he had inherited, and then decided to implement a very similar plan to his predecessor. General Eichelberger realised that clearing the Japanese off the ridge north of Mokmer Airfield was more important than the easy seizure of Borokoe and Sorido Airfields.
During the first half of June the Japanese made three attempts to move a major convoy to Biak, the KON Force. All three attempts failed, although around 100-200 men did reach the islands. During the same period around 1,000 men probably reached the island by barge. Most of these troops were used to garrison the ridge north of Mokmer airfield. In response to these Japanese efforts, on 13 June General Fuller asked for reinforcements. One regiment from the 24th Division at Hollandia was chosen, but it would be General Eicheberger who got the benefit of the new unit.
The American attack resumed on 16 June, this time with the 2nd Battalion, 186th Infantry in the lead. This time the Japanese resistance was overcome, and the last part of the low ridge south of the West Caves was cleared in two hours, but progress after that was slow. By the end of the day the West Caves were almost surrounded, but General Doe was worried about the exposed position of some of his men and ordered them to retreat to the low ridge area. The attack was resumed on 17 June and some progress was made in an area overlooking the West Caves.
After the attack on 17 June General Eichelberger decided to cancel the next part of General Doe's attack, and prepare for a larger scale offensive using the full strength of the 162nd and 186th Regiments, to start on 19 June. The 186th was to make the main attack on the West Caves, with two battalions attacking from the west and one from the east. By the end of the day this attack had surrounded the West Caves, and the Americans prepared for two operations on 20 June - one aimed at the Japanese in the West Caves and the other heading further into the high ground overlooking the airfields. On 21 June the main effort was mounted against the strongest cave positions in the West Caves. The main cave was attacked by pouring fuel into the caves and setting it alight. On the night of 21-22 June the surviving Japanese defenders of the caves launched an attack on the US lines in an attempt to escape from the area. Three attempts were made and all three were repulsed. Japanese sources suggest that this attack was triggered by Colonel Kuzume after he decided that the battle was lost, and ordered his men to attempt to escape to the north and west. The colonel was probably killed in combat a few days later. This didn't end resistance in the West Caves area, and on 22 June heavy demolition charges were used to try and seal the entrances. A few survivors were encountered over the next few days, and the area wasn't entirely cleared until 27 June.
The fighting in the West Caves had finally removed the last Japanese barrier to operations on Mokmer Field. On 22 June the first P-40s began to operate from the airfield. The focus then moved on to securing the other two airfields and pushing the Japanese further away from the airfield area. General Eichenberger was happy that the main part of the job was now completed and handed command over to General Doe on 28 June. Doe almost immediately lost the 34th Infantry, which was about to recalled to prepare for another campaign. On the same day the Japanese received new orders of their own when the 2nd Area Army ordered the Biak Detachment to prepare for guerrilla warfare. In fact the detachment had suffered so heavily by the end of June that they were unable to follow this order, and consistent American patrols denied them the change they needed to change their role.
The first major attack on the East Caves began on 3 July when engineer supported by tanks sealed up some of the tunnel entrances. Over the next few days the Americans pushed further into the area, only to discover that the Japanese had evacuated the area. The East Caves were quickly secured, although isolated Japanese troops continued to pop up until 20 July.
There had been combat in the Ibdi Pocket since the start of June, and US infantry operated in the area until 28 June, slowly pushing the Japanese west. After that they carried out a mix of patrols and artillery bombardments. This weakened the defences and also cleared some of the jungle. On 11 July the 3rd Battalion, 163rd Infantry began a new phase of infantry operations. These lasted until 22 July when the commander of the 3rd Battalion announced that organised resistance was over. Mopping up operations took another week.
At the end of July there were still 4,000 Japanese troops on the island. During August the Americans conducted vigorous patrolling in order to prevent them from reorganising their forces. The Japanese had orders to move to Wardo Bay on the west coast, but on 17 August the 1st Battalion, 186ht Infantry, landed at that bay. Some Japanese troops were ambushed as they approached the bay, others broke and scattered into the interior and concentrated on survival.
Attempts to Reinforce Biak and the Battle of the Philippine Sea
By the summer of 1944 the Japanese realised that their plans were in chaos and had decided to try and provoke a major naval battle in which they would inflict heavy damage on the US fleet and at best convince the Americans to negotiate or at worse delay their advance. This plan, Operation A-Go, relied on land aircraft to support the increasingly outnumbered carrier force, and the aim was to fight it somewhere in the Philippine Sea, ideally in the western part of the sea, near as many land based aircraft as possible. All they needed was a way to draw out the American fleet, and the landings on Biak were seen as one such opportunity. However this did mean that the island would have to be held long enough to allow the Combined Fleet to arrive in the area.
In order to achieve this, the Japanese made three attempts to get reinforcements onto Biak. The 2nd Amphibious Brigade was to be moved form the Philippines as Operation Kon, while the companies of the 35th Division were to be moved from Sorong.
The first Kon convoy turned back on 3 June after a false report that US carriers were in the area. This came from Japanese reconnaissance pilots who appear to have mistaken LSTs for carriers. The second Kon convoy did reach Biak, this time probably carrying men from the 35th Division, but only landed 100 troops before being forced to retreat by the arrival of a strong American naval task force on the night of 8-9 June.
The third Kon operation was the most serious, and was supported by part of the Combined Fleet, including the giant battleships Yamato and Musashi. This fleet would have outclassed any American naval forces in the area, and could have inflicted heavy damage on the landings forces, but on 15 June the Americans invaded the Mariana Islands. This posed a direct threat to the Japanese Home Islands. Operation A-Go was ordered in effect. The relief convoy was ordered north to join up with the rest of the fleet and the combined fleet then steamed east to defeat at the Battle of the Philippine Sea (19-20 June 1944), the last major carrier battle of the Pacific War.