'Straightline' was the US seizure of Wakde island and Sarmi on the north coast of Japanese-occupied western New Guinea (17/21 May 1944).

Wakde is an island with a small anchorage just off the northern coast of New Guinea. The Japanese occupied the island in 1942 and had completed an airfield, with a crushed coral runway, by 1943. By a time early 1944 the Japanese had also completed an airstrip at Sawar on the mainland to the west of Wakde island and had a second under construction at Maffin Bay, just to the east of Sawar. The headquarters of Lieutenant General Hachiro Tagami’s 36^th Division was established at Sarmi, in whose immediate area there were about 11,000 Japanese soldiers, perhaps half of them combat troops.

The 'Straightline' undertaking was the logical successor to the 'Reckless' operation against Hollandia in the fast-moving westward advance of the forces of General Douglas MacArthur’s South-West Pacific Area command, and was undertaken while the last stages of the 'Reckless' and parallel 'Persecution' operations against Hollandia and Aitape were still under way.

On 12 March 1944, MacArthur had been ordered by the Joint Chiefs-of-Staff Committee to take Hollandia in order to establish heavy bomber bases from which the southern flank of Admiral Chester W. Nimitz’s drive through the central Pacific could be protected. It became clear shortly after the Hollandia landings, however, that it would require many months to prepare the runways for heavy bombers, and aerial reconnaissance had identified no other suitable site closer than the island of Biak farther to the west. MacArthur therefore ordered rapid planning for an invasion of the area of Wakde and Sarmi as a preliminary to the assault on Biak some 10 days later.

The initial orders were issued on 27 April and envisaged the delivery of the assault on 15 May. Rear Admiral William M. Fechteler, the deputy commander of the 7^th Amphibious Force, was to head the naval forces and the ground force would be built around Major General Horace H. Fuller’s 41^st Division. As a result of an acute shortage of shipping, however, the invasion was later delayed to 17 May and the invasion force was pared down to 7,800 men of the reinforced 163^rd Regimental Combat Team under the command of Brigadier General Jens A. Doe, the assistant divisional commander of the 41^st Division, the bulk of whose strength was to be committed to the Biak landing on 27 May. Captain Albert G. Noble was designated to lead the scaled-down naval forces in place of Fechteler.

The details of 'Straightline' were planned by Lieutenant General Walter C. Krueger’s 6^th Army with the double object of providing Lieutenant General George C. Kenney’s 5^th AAF with an area suitable for heavy bomber bases, and of denying Lieutenant General Hatazo Adachi’s 18^th Army a fall-back position for Lieutenant General Fusataro Teshima’s 2^nd Army after its pending defeat at Hollandia and Aitape.

Wakde (actually called Insoemaar and one of two islands comprising the Wakde islands, but always called Wakde by the US forces) had recently seen the construction of a Japanese airstrip. Lying some 120 miles (195 km) to the west of Hollandia but just 2 miles (3.2 km) offshore near Toem and Sarmi, the island was admirably suited to MacArthur’s 'coast-hopping' progress, especially as a mainland airstrip had been built at Toem and a third was under construction. The area was held by Tagami’s 36^th Division (223^rd and 224^th Regiments but not its 222^nd Regiment, which had been detached to Biak island), the Japanese strength being boosted to 14,000 troops including the 4^th Engineer Group (anti-aircraft, airfield and service troops) and the Japanese navy’s 91^st Garrison Force. The Japanese strength had been reduced recently to 11,000 men, however, as General Korechika Anami’s 2^nd Area Army had instructed the 'Matsuyama' Force, comprising much of the 224^th Regiment, to develop and hold a blocking position farther to the east at Armopa, a point about mid-way between Hollandia and Sarmi.

The Allies estimated that the Japanese had 6,500 men in the area of Sarmi and Wakde, but while this figure was too low, the Allies were more accurate with their estimate of 4,000 combat troops.

Under the overall control of Fechteler’s Task Force 77 in Vice Admiral Thomas C. Kinkaid’s US 7^th Fleet, Noble’s Task Group 77.2 was entrusted with the transport and landing of the 163^rd Regimental Combat Team in the transport Henry T. Allen, Australian infantry landing ship Manoora and 11 infantry landing craft screened by the destroyers Gillespie, Grayson, Hobby, Kalk, Nicholson, Reid, Roe, Stevenson, Stockton, Trathen, Welles and Wilkes, and the destroyer escorts Eichenberger, James E. Craig, Lovelace, Manning and Neuendorf, and with support by the fleet tugs Reserve and Sonoma, four submarine chasers and three rocket-firing infantry landing craft.

Cover for the transport and landing force was provided by Covering Force 'A' and Covering Force 'B'. The former was TF74 under the command of the British Rear Admiral V. A. C. Crutchley with the Australian heavy cruisers Australia and Shropshire, the Australian destroyers Arunta and Warramunga, and the US destroyers Ammen and Mullany, and the latter was TF75 under the command of the US Rear Admiral Russell S. Berkey with the light cruisers Boise, Nashville and Phoenix, and destroyers Abner Read, Bache, Beale, Bush, Daley and Hutchins of Destroyer Squadron 24.

Also available in support were the aircraft of TF73 (Aircraft 7^th Fleet) in the form of Task Group 73.1 (Seeadler Harbour Group) with the seaplane tender Tangier and small seaplane tenders Heron and San Pablo with the 26 Consolidated PBY-4 Catalina flying boats of the VP-33 and VP-52 squadron, and the 11 Consolidated PB4Y-1 maritime patrol bombers of the VB-106 squadron, and of TG73.2 (Langemak Bay Group) with the small seaplane tender Half Moon with the 10 PBY-5 flying boats of the VP-34 squadron.

As noted above, the unit entrusted with the landing was Doe’s reinforced 163^rd Regimental Combat Team of Fuller’s 41^st Division, the formation which had spearheaded the 'Persecution' operation. The US reserves were the 128^th Infantry of Major General William H. Gill’s 32^nd Division, and the separate 158^th Infantry.

The Japanese base complex had been attacked by US carrierborne aircraft on 21 April in preparation for the Hollandia invasion, and the only resistance the aircraft encountered was scattered anti-aircraft fire. More attacks were carried out by land-based bombers from 28 April onward, and these were supplemented by the gunfire bombardments of Berkey’s TF75 from 29 April. Weather then interfered with air operations until 13 May, when the US 5^th AAF resumed heavy attacks on Wakde and Biak.

A landing flotilla of two transports and 11 LCIs started to embark the 163^rd Regimental Combat Team at Aitape on 15 May, and the whole attack group assembled at Hollandia on the following day, covered by Crutchley’s and Berkey’s cruiser forces. The Allies correctly estimated that Imperial Japanese navy was otherwise preoccupied with preparations for the decisive 'Sho' battles off the Mariana island and Philippine island groups, and would therefore make no major effort to interfere.

Tagami had deployed 763 of his troops on Wakde island and spread another 1,700 men along the coast opposite the island, with the remainder deployed between Sawar and Sarmi.

'Straightline' began on 17 May with an unopposed landing, which took Togami completely by surprise, at the village of Arare after the Japanese positions had been bombarded for almost an hour by a force of five light cruisers and 10 destroyers, followed by a rocket bombardment of the landing beaches by two of the LCI(R) vessels. The Americans quickly secured a beach-head and deployed artillery to support the landings on Wakde island, which were scheduled for the next day. The Americans also landed on the islet of Insoemanai, just to the south of Wakde, where mortars and heavy machine guns positions were established. On the mainland, the Americans then advanced to Toem, opposite Wakde island.

On the following day US artillery was lined up on the New Guinea shore to support the naval gunfire of two destroyers in support of the landings on Wakde island in the landing craft of the 3^rd Engineer Special Brigade delivered the 163^rd Regimental Combat Team onto Wakde after the unopposed landing at nearby mainland village of Arare. The Japanese defenders occupied 100 pillboxes and bunkers as well as 12 caves, and 20-mm aircraft cannon were mounted in some of the pillboxes.

The landings at 09.30 were achieved without incident as the Japanese defensive weapons were blanketed by the rocket barrage of the three adapted infantry landing craft, but as it attempted to push inland the 163^rd Regimental Combat Team was met by determined Japanese opposition. The engineers tasked with developing the island’s airfield for US service followed the infantry so closely that they came under sniper fire. It took the Americans 2.5 days to overrun the island, which measures 2 miles (3.2 km) in length and 1 mile (1.6 km) in width, and at the end there were only four survivors of the Japanese garrison. The cost to the US forces was 40 men killed and another 107 wounded.

On 19 May the Kumamba islands, to the north of Sarmi, were occupied without meeting any opposition, and this allowed the siting of radar equipments to provide early warning for Wakde of any Japanese air attacks.

The airstrip of Wakde island had come into use by tactical aircraft by 12.00 on 21 May, in time to support the coastal drive launched by the 41^st Division at the insistence of Krueger. By 27 May Consolidated B-24 Liberator heavy bombers based on Wakde were flying reconnaissance missions over Mindanao, at that time slated to be the location of the US return to the Philippine islands group. Wakde was used by large numbers of aircraft for several months thereafter, but by December 1944 the Allied counter-offensive had moved considerably farther through the Japanese strategic perimeter and Wakde was reduced to an emergency airfield.

Continued US operations in the area of Toem and Sarmi reflected the reasoning of Krueger, the 6^th Army’s commander, that the 10,000 or so men of the 36^th Division constituted a serious threat to the US retention of Wakde island. Krueger wrongly thought that the positions of the 36^th Division were weak, and the 158^th Regimental Combat Team suffered heavy losses in an unsuccessful four-day effort to take a feature known as Lone Tree Hill.

After their loss of Hollandia, to the east, to the US forces in April 1944, the 26 miles (42 km) of coast and surrounding area bounded by Toem, Wakde and Sarmi, was in effect an isolated Japanese coastal salient. Even so, elements of the 223^rd Regiment and 224^th Regiment, under Tagami’s command, were concentrated at Lone Tree Hill, overlooking Maffin Bay, and were blocking any further advance by the 158^th RCT. The Japanese held well-prepared positions, which included fortified caves. Meanwhile, the main body of the 223^rd Regiment had outflanked the US units, and one battalion of the 224^th Regiment was retreating from Hollandia in the direction of the area bounded by Toem, Wakde and Sarmi.

Lone Tree Hill rises from a flat, coastal plain about 2,000 yards (1830 m) to the west of the main jetty in Maffin Bay. The hill was named for a single tree depicted on its crest by US maps; it was a coral formation, covered with dense tropical rain forest and undergrowth. It is about 175 ft (53 m) high, 1,200 yards (1095 m) long on its north/south axis and 1,000 yards (915 m) wide on its east/west axis. The northern side was characterised by a steep slope, and the eastern slope was fronted by a short, twisting stream known to the US force as the Snaky river.

On 14 June, Krueger, sent Sibert’s 6^th Division to relieve the 158^th RCT, and there followed about one month before combat was rejoined. In a period of 10 days. including three days of very severe fighting, the US formation took Lone Tree Hill. The final Japanese resistance in this area was not overcome until the beginning of September after the Japanese had lost another 3,870 men killed, including some trapped in caves, and the Americans 400 men killed and another 1,500 wounded and 15 missing in this vicious jungle fighting in the Trier mountains. With Lone Tree Hill in American possession, Maffin Bay became a major staging base for six subsequent battles at Biak ('Horlicks'), Noemfoor ('Cyclone'), Sansapor ('Globetrotter'), Leyte ('King II') and Luzon ('Mike').

Krueger sensibly decided to halt his offensive effort at this point, and Sarmi remained in Japanese hands until the end of the war.

On 31 May, two battalions of the 163^rd Regimental Combat Team were pulled off Wakde island and rushed to Biak island, where the other elements of the 41^st Division had landed four days earlier in 'Horlicks'. On 1 September the 123^rd Regimental Combat Team of Major General Percy W. Clarkson’s 33^rd Division relieved the last elements of the 41^st Division and patrolled Wakde airfield and the Toem-Sarmi sector until 26 January 1945.

On 6 June 1944 the Japanese returned to Wakde, this time as the attackers. Three Mitsubishi G4M 'Betty' bombers of the Japanese navy’s 732^nd Kokutai took off from Wasile farther to the west on the night of 5/6 June, but only two of the aircraft attacked Wakde as the third had become separated during the adverse weather of that night. The two bombers which did succeed in finding Wakde located a break in the clouds which allowed them to sight the airfield and swoop down low on this target area. Each bomber took one side of the runway along which US aircraft were parked. Releasing their bombs in a string over the parked aircraft, the Japanese crews estimated they had destroyed dozens of US aircraft. Later reconnaissance photographs seemed to show 76 aircraft burned or damaged.

The fighting in 'Straightline' had been particularly severe, the Americans losing 646 dead and the Japanese some 3,899 dead, a ratio in favour of the Americans of 1/6, the lowest of the 'coast-hopping' campaign. It had by then been discovered that the area was unsuitable for heavy bombers (as was the Sentani airfield complex at Hollandia), so MacArthur moved boldly forward to Biak with the balance of the 41^st Division even as part of that formation was still fighting its way forward to Sarmi.