The Battle of Kaiapit was an action fought in 1943 between Australian and Japanese forces in New Guinea during the Markham and Ramu Valley – Finisterre Range campaign of World War II.

Following the landings at Nadzab and at Lae, the Allies attempted to exploit their success with an advance into the upper Markham Valley, starting with Kaiapit.

The Australian 2/6th Independent Company flew in to the Markham Valley from Port Moresby in 13 USAAF C-47 Dakotas, 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 to secure the area so that it could be developed into an airfield.

It accomplished the 7th Division's primary mission, for the Japanese could no longer threaten Lae or Nadzab, where a major airbase was being developed.

The victory also led to the capture of the entire Ramu Valley, which provided new forward fighter airstrips for the air war against the Japanese.

[1] Following the landing at Nadzab, General Sir Thomas Blamey, the Allied Land Forces commander, intended to exploit his success with an advance into the upper Markham Valley, which would protect Nadzab from Japanese ground attack, and serve as a jumping off point for an overland advance into the Ramu Valley to capture airfield sites there.

Even flying in an airborne engineer aviation battalion to improve the airstrip would have involved taking aircraft away from operations supporting the 7th Division at Nadzab.

However, Herring calculated that the 7th Division had sufficient reserves at Nadzab to allow maintenance flights to be suspended for a week or so after the capture of Kaiapit.

[5] Lieutenant Everette E. Frazier, USAAF, selected a level, burned-off area near the Leron River, not far from Kaiapit, and landed in an L-4 Piper Cub.

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.

Powered by lead-acid batteries which were recharged with petrol generators, it required multiple signallers to carry and the noise was liable to attract the attention of the enemy.

[8] For three days in a row, the 2/6th Independent Company prepared to fly out from Port Moresby, only to be told that its flight had been cancelled due to bad weather.

That evening Chalk and King received airdropped messages from Vasey instructing them to occupy Kaiapit as soon as possible, and prepare a landing strip for troop-carrying aircraft.

[13] From Kaiapit it 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 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.

[14] Yonekura's main body, moving by night to avoid being sighted by Allied aircraft, was by this time no further from Kaiapit than King, but had two rivers to cross.

[15] King assembled his troops at Sangan, about 16 km (9.9 mi) south of Kaiapit, except for one section under Lieutenant E. F. Maxwell that had been sent ahead to scout the village.

The going was relatively easy insofar as the ground was fairly flat, but the 2 m (6.6 ft) high kunai grass trapped the heat and humidity and the men were heavily loaded with ammunition.

[22] Lieutenant Derrick Watson's C Platoon set out at around 06:15 and advanced to the edge of Village 3, a distance of about 200 yd (180 m), before becoming pinned down by heavy Japanese fire.

[24] He led his section in an advance across 70 yd (64 m) of open ground, and attacked three Japanese machine gun posts with hand grenades.

By the time engineering surveys of the area had been completed, as a direct consequence of the victory at Kaiapit, Dougherty's men had captured Gusap.

There, 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.

The airstrip at Gusap "paid for itself many times over in the quantity of Japanese aircraft, equipment and personnel destroyed by Allied attack missions projected from it.

As a result of the Moscow Declaration, the Minister for External Affairs, Dr. H. V. Evatt, commissioned a report by William Webb on war crimes committed by the Japanese.

Webb took depositions from three members of the 2/6th Independent Company about the Kaiapit incident which formed part of his report, which was submitted to the United Nations War Crimes Commission in 1944.

It opened the gate to the Ramu Valley for the 21st Infantry Brigade, provided new forward fighter airstrips for the air war against the Japanese,[29] and validated the Australian Army's new training methods and the organisational emphasis on firepower.

[39] He confided to Herring that he felt that he had made a potentially disastrous mistake: "it is quite wrong to send out a small unit like the 2/6th Independent Company so far that they cannot be supported.

[41] Japanese historian Tanaka Kengoro said that the mission of the Nakai Detachment achieved the objective of threatening Nadzab so as to draw Allied attention away from the troops escaping from Lae.

The 2/6th Independent Company proved to be an ideal unit for the mission, as it combined determined leadership with thorough training and effective firepower.