The 'Action at Kaiapit' was fought between Australian and Japanese forces between Australian and Japanese forces in New Guinea during the Markham and the Ramu valley and Finisterre range campaign (19/20 September 1943).

Following the US airborne landings at Nadzab and Australian amphibious landings at Lae within the early stages of 'Postern', the Allies attempted to exploit their success with an advance up the Markham river valley, starting with Kaiapit. The Japanese intended to use Kaiapit to threaten the Allied position at Nadzab, and to create a diversion to allow the Japanese garrison at Lae time to escape.

The Australian 2/6^th Independent Company flew into the Markham river valley from Port Moresby in 13 Douglas C-47 Skytrain twin-engined transport aircraft of the USAAF, making a difficult landing on a rough airstrip. Unaware that a much larger Japanese force was also headed for Kaiapit, the company attacked the village on 19 September in order to secure the area for development into an airfield. The company then held it against a strong counterattack. During two days of fighting the Australians defeated a larger Japanese force while suffering relatively few losses.

The Australian victory at Kaiapit enabled Major General G. A. Vasey’s Australian 7^th Division to be flown in to the upper part of the Markham river valley. This accomplished the 7^th Division’s primary mission, for the Japanese could no longer threaten Lae or Nadzab, where a major air base was being developed. The victory also led to the capture of the entire Ramu river valley, which provided new forward fighter airstrips for the air war against the Japanese forces in New Guinea.

The Markham river valley is part of a long, flat depression varying from 5 to 20 miles (8 to 32 km) in width, and cuts through the otherwise mountainous terrain of the interior of New Guinea, extending from the mouth of the Markham river near the port of Lae on the Huon Gulf to that of the mouth of Ramu river 370 miles (600 km) away. The two rivers flow in opposite directions, separated by a divide about 80 miles (130 km) upstream from Lae. The area is flat and suitable for airstrips, although it is intercut by many tributaries of the two main rivers. Between the Ramu river valley and Madang, on the north coast of New Guinea, lies the rugged Finisterre mountain range.

Following the landing at Nadzab, General Sir Thomas Blamey, the commander of the Allied land forces in New Guinea, intended to exploit his success with an advance into the upper part of the Markham river valley, which would protect Nadzab from Japanese ground attack and also serve as a jumping off point for an overland advance into the Ramu river valley for the seizure of airfield sites there. On 16 September, which was the day on which Lae fell to the Allies, Lieutenant General Sir Edmund Herring, commander of the I Corps, Vasey, the commander of the 7^th Division, and Major General Ennis Whitehead, the commander of the Advanced Echelon, US 5^th Army Air Force, met at Whitehead’s headquarters. Whitehead wished to establish fighter airstrips in the Kaiapit area by 1 November in order to bring short-range fighters within range of the major Japanese base at Wewak on the north coast. The 7^th Division’s mission was to prevent the Japanese at Madang from using the Markham and Ramu river valleys to threaten Lae or Nadzab. Vasey and Herring considered both an overland operation to capture Dumpu, in the Ramu river valley, and an airborne operation using paratroopers of the US 503^rd Parachute Infantry. Blamey did not agree with their idea of capturing Dumpu first, insisting that Kaiapit be taken beforehand.

Until a road could be opened from Lae, the Kaiapit area could be supplied only by air, and the Allies possessed only a limited number of transport aircraft. Even flying in an airborne engineer aviation battalion to improve the airstrip would have involved taking aircraft away from operations supporting the 7^th Division at Nadzab. Moreover, Whitehead warned that he could not guarantee adequate air support for both Kaiapit and the operation to take Finschhafen at the same time. However, Herring calculated that the 7^th Division had sufficient reserves at Nadzab to allow maintenance flights to be suspended for a week or so after the capture of Kaiapit. He planned to seize Kaiapit with an overland advance from Nadzab by independent companies, the Papuan Infantry Battalion and Brigadier I. N. Dougherty’s 21^st Brigade of the 7^th Division.

The airstrip at Kaiapit was reconnoitred on 11 September 1943 by No. 4 Squadron RAAF, which reported that it was apparently in good condition, with the kunai grass recently cut. Lieutenant Everette E. Frazier of the USAAF selected a level and burned-off area near the Leron river, not far from Kaiapit, and landed in a Piper L-4 single-engined lightplane. Frazier determined that it would be possible to land a C-47 there, and on 16 September Hutchison approved the site for C-47 to land.

The 2/6^th Independent Company had arrived in Port Moresby from Australia on 2 August. The unit had fought in Papua in 1942 in the Battle of Buna and Gona, and had since undertaken high-intensity training in Queensland. The company was under the command of Captain Gordon King, who had been its second in command at Buna. King received a warning order on 12 September alerting him to prepare for the capture of Kaiapit, and had access to detailed aerial photographs of the area.

The typical independent company of the time had a nominal strength of 20 officers and 275 other ranks. Larger than a conventional infantry company, it was organised into three platoons, each of three sections, each of which contained two sub-sections. The company had considerable firepower. Each sub-section had a Bren light machine gun, and the machine gunner’s two assistants carried rifles and extra 30-round Bren gun magazines. A sniper also carried a rifle, as did one man equipped with rifle grenades. The remaining four or five men carried Owen sub-machine guns. Each platoon also had a section of 2-in (51-mm) light mortars.

The company was self-supporting, with its own engineer, signals, transport, and quartermaster sections. The signals section had a powerful but cumbersome radio set for communicating with the 7^th Division. Powered by lead-acid batteries, which were recharged by petrol generators, the radio had to be carried by several signallers and the noise was liable to attract Japanese attention. The platoons were equipped with a newer radio, which was a smaller and more portable set developed for the communication needs of units on the move in jungle conditions. However, the 2/6^th Independent Company had not had time to work with them operationally.

For three days, the 2/6^th Independent Company prepared to fly out from Port Moresby only to be told that its flight had been cancelled as a result of adverse weather. On 17 September, 13 C-47 aircraft of the US 374^th Troop Carrier Group finally took off for Leron. King flew in the leading aeroplane and as the aeroplane came in to land, King spotted patrols of the Papuan Infantry Battalion in the area.

One of the C-47 aircraft blew a tyre as it touched down on the rough airstrip. Another tried to land on one wheel but the landing gear collapsed and the aeroplane thus belly-landed. The former machine was subsequently salvaged, but the latter was a total loss. King sent out patrols that soon located Captain J. A. Chalk’s B Company, Papuan Infantry Battalion. That evening Chalk and King received air-dropped messages from Vasey instructing them to occupy Kaiapit as soon as possible and to ready a landing strip for troop-carrying aircraft. Vasey informed the two officers that only small Japanese parties escaping from Lae were in the area, and that their morale was very low. Vasey flew in to Leron on 18 September to meet with King, whom he ordered to '[g]o to Kaiapit quickly, clean up the Japs and inform division.;

As it happened, Major General Masutaro Nakai, commander of the 20^th Division's infantry group, had ordered a sizeable force to move to Kaiapit under the command of Major Yonekura Tsuneo. The latter’s force included the 9^th Company and 10^th Company of the 78^th Regiment, the 5^th Company of the 80^th Regiment, one heavy machine-gun section, one signals section and one engineer company, in total about 500 men. From Kaiapit this force was to threaten the Allied position at Nadzab, creating a diversion to allow the Japanese garrison at Lae time to escape. The main body left Yokopi in the Finisterre mountain range on 6 September but was delayed by heavy rains that forced the troops to move, soaking wet, through muddy water for much of the way. Only the force’s advance party had reached Kaiapit by 18 September, by which time Lae had already fallen. Yonekura’s main body, moving by night to avoid being sighted by Allied aircraft, was by this time no farther from Kaiapit than King, but had two rivers to cross.

King assembled most of his unit at Sangan, about 10 miles (16 km) to the south of Kaiapit, the exception being one section under Lieutenant E. F. Maxwell that had been sent ahead to scout the village. On the morning of 19 September, King set out for Kaiapit, leaving behind his quartermaster, transport and engineering sections, which would move the stores left behind at the Leron river first to Sangan and then to Kaiapit on 20 September. King took one section of Papuans with him, leaving Chalk and the rest of his men to escort the native carriers bringing up the stores.

King’s men walked for 50 minutes at a time and then rested for 10 minutes. The going was relatively easy insofar as the ground was fairly flat, but the kunai grass, which was some 6.5 ft (2 m) high, trapped the heat and humidity and the men were heavily loaded with ammunition. The company reached Ragitumkiap, a village within striking distance of Kaiapit, at 14.45. While his men had a brief rest, King attempted to contact the large radio set he had left at Sangan, and then Vasey back at Nadzab with the newer radios he had brought with him, but found that their range was insufficient. He also heard shots in the distance and guessed that Maxwell’s section had been discovered.

The 2/6^th Independent Company formed up at 15:15 in kunai grass about 1,300 yards (1200 m) from Kaiapit. As the company advanced it came under fire from foxholes on the edge of the village. A 2-in (51-mm) mortar bomb knocked out a Japanese light machine gun, and the foxholes were outflanked and taken out with hand grenades and bayonets. The Japanese then pulled back, leaving 30 dead. The Australians suffered two men killed and seven wounded, the latter including King, who was lightly wounded.

The company then established a defensive position for the night, and as it was doing so Lieutenant D. B. Stuart, the commander of one of the Papuan platoons, arrived. The Papuans had become concerned when radio contact had been lost and Stuart had been sent to find out what was happening. King ordered Stuart to bring the Papuans up from Sangan with extra ammunition and the older radio set. At around 17.30, a native arrived with a message intended for the Japanese commander. The paper was taken from him and he was shot when he tried to escape. Later, a Japanese patrol returned to Kaiapit, unaware that it was now in Australian hands, and its men were killed when they stumbled across a Bren gun position. Four more Japanese soldiers returned after 00.00, and one of them escaped.

Yonekura and his men had reached Kaiapit after an exhausting night march. Yonekura was aware that the Australians had reached Kaiapit but his main concern was not to be caught in the open by Allied aircraft. Spotting Australian positions in the pre-dawn light, the Japanese column opened fire on the Australians, who replied sporadically as they sought to conserve their ammunition. Although he was running short of ammunition, King launched an immediate counterattack, which took the Japanese by surprise.

Lieutenant Derrick Watson’s C Platoon set out at about 06.15 and had advanced to the edge of Village No. 3, a distance of about 200 yards (180 m), before becoming pinned down by heavy Japanese fire. King then sent Captain Gordon Blainey’s A Platoon around the right flank toward the high ground on Mission Hill, which overlooked the battlefield, and this feature had been secured by 07.30. In the meantime, some of the 2/6^th Independent Company’s signallers and headquarters personnel gathered together what ammunition they could, and delivered it to C Platoon at about 07.00. C Platoon then fixed bayonets and continued its advance.

The commander of C Platoon’s No. 9 Section, Lieutenant Bob Balderstone, led his section in an advance across 70 yards (65 m) of open ground and attacked three Japanese machine gun positions with hand grenades. Lieutenant Reg Hallion led A Platoon’s No. 3 Section against the Japanese positions at the base of Mission Hill, and was killed in an attack on a machine gun post, but his section captured the position and killed 12 Japanese. By 10.00, the action was over.

After the action, King’s men counted 214 Japanese bodies, and estimated that another 50 or more lay dead in the kunai grass. Yonekura was among the dead. The Australians suffered 14 men killed and 23 wounded. Equipment abandoned by the Japanese included 19 machine guns, 150 rifles, six grenade throwers and 12 swords.

The 2/6^th Independent Company had won a significant victory, but now had 23 wounded and was very short of ammunition. Frazier landed on the newly captured airstrip in his L-4 at 12.30, rejected the airstrip as unsuitable for the C-47, and oversaw the preparation of a new airstrip on better ground near Mission Hill. This was characterised by a difficult approach, as aircraft had to land upwind while avoiding Mission Hill. Although it was not known if the airstrip would be ready, Hutchison flew in for a test landing on the following day at 15.30. He collected the wounded and flew them to Nadzab, and returned an hour later with a load of rations and ammunition as well as Dougherty and his brigade headquarters. At about 18.00, six more transport aircraft arrived.

Vasey was concerned for the security of the Kaiapit area as he believed that the Japanese were inclined to continue with a plan once it was in motion. Exploiting the good flying weather on 22 September, 99 round trips were made between Nadzab and Kaiapit. Most of the 2/16^th Battalion and some US engineers were flown in. The 2/14^th Battalion and a battery of the 2/4^th Field Regiment arrived on 25 September, and Brigadier K. W. Eather’s 25^th Brigade began to arrive two days later, freeing Dougherty’s brigade to advance on Dumpu.

Kaiapit did not become an important air base. By the time engineering surveys of the area had been completed, as a direct consequence of the victory at Kaiapit Dougherty brigade had captured Gusap, and here the engineers found a well-drained area with soil conditions suitable for the construction of all-weather airstrips, an unobstructed air approach and a pleasant climate. It was therefore decided to limit construction at the swampy and malarial Kaiapit and concentrate on Gusap, where the US 871^st, 872^nd and 875^th Airborne Aviation Engineer Battalions constructed 10 airstrips and numerous ancillary facilities. Although some equipment was carried on the overland trek, most of it had to be flown in and nearly all of it was worn out by the time the work had been completed. The first Curtiss P-40 Kittyhawk single-engined fighter squadron began operating from Gusap in November and an all-weather fighter runway had been completed in January 1944. The base at Gusap proved invaluable as aircraft using it destroyed large numbers of Japanese aircraft as well as much equipment and many men.

Thus the 2/6^th Independent Company had defeated the vanguard of Nakai’s force and stopped his advance down the Markham river valley. The 'Action at Kaiapit' therefore accomplished Vasey’s primary mission, for the Japanese could no longer threaten Nadzab. The success opened the gate to the Ramu river valley for the 21^st Brigade, provided new forward fighter airstrips for the air war against the Japanese, and validated the Australian army’s new training methods and the organisational emphasis on firepower.

The Japanese believed that they had been attacked by an Australian force of 'unexpected strength'.