Lieutenant Colonel F. H. Sublet's  2/16th Infantry Battalion, a unit from Western Australia, arrived at Kaiapit on 22 September.
It set out at 15:00 that afternoon, crossing the Maniang River, which had a series of channels, extending across 2,000 yards (1,800 m).
Its patrols attempted to locate the Japanese, as did aircraft from No.
4 Squadron RAAF.
Only one saw any, the 12 Platoon, under Lieutenant J. R. Walder, which spotted three Japanese soldiers on the far side of the Umi River who fled when fired upon.
Wallder's 12 Platoon, and 17 Platoon under Captain K. McCullough, crossed the Umi, which was about 50 yards (46 m) wide, up to 5 feet 6 inches (1.68 m) deep at the crossing point, and swift-flowing, and headed for Sagerak.

The 2/27th Infantry Battalion, a South Australian unit under the command of Lieutenant Colonel J. A. Bishop, arrived at Kaiapit on the morning of 23 September, having flown directly from Jacksons and Wards at Port Moresby in 45 USAAF C-47 transport aircraft, escorted by P-47 Thunderbolt, P-38 Lightning and P-39 Airacobra fighters.
The first C-47 arrived at Kaiapit at 09:00 and the last at 10:50.
Each took about ten minutes to unload all its troops and stores.
The 2/27th took over the defence of Kaiapit from the 2/6th Independent Company.
No aircraft arrived on 24 September, leaving Dougherty without the 2/14th Infantry Battalion, which was still back at Nadzab, and with only the rations and ammunition that the 2/16th and 2/27th had brought with them.

The pioneer platoon of the 2/16th strung a rope across the Umi River, allowing the heavily equipped diggers of B and C Companies to cross the fast-flowing torrent.
They were across by 12:30, but the entire 2/16th did not complete the crossing until 20:00.
On the other side, contact was made with Japanese units, and 12 Platoon came under light machine gun fire, but drove the Japanese off with its 2-inch mortars.
When 17 Platoon was engaged by light machine guns, it used its 2-inch mortars to lay smoke, allowing it to withdraw.
By 14:40, the leading platoon, 10 Platoon under Lieutenant W. J. Duncan, was overlooking Sagerak, but Duncan was wounded by a sniper at 17:00.
Sublet ordered B Company to halt on the high ground, with the intent of attacking Sagerak the next day.

At 20:30, just a half-hour after it had completed the crossing of the Umi, the 2/16th received orders from Dougherty to pull back.
With considerable lack of enthusiasm, the 2/16th re-crossed the Umi, this time in the dark.
Re-crossing commenced at 03:00 and was completed by 08:00.
Lieutenant R. G. Crombie's 11 Platoon was left behind on the high ground overlooking Sagerak.
It entered Sagerak that morning, and found it deserted.
About 16 Japanese soldiers fled when upon their approach, leaving behind their documents, medical stores and equipment.
Lieutenant Everette E. Frazier, an American aviation engineer, pegged out a landing strip nearby and had it ready to receive C-47s in four hours.

Vasey flew into Kaiapit to talk to Dougherty.
He explained that the reason for halting the 2/16th was an appreciation that Adachi would persist with his original plan, known to the Australians through documents captured at Kaiapit, even though it had been overtaken by events.
Vasey believed that the open area between the Umi and Kaiapit would be an excellent place to destroy the Japanese force, should it choose to attack.
He therefore proposed to halt for a while, reinforcing the position at Kaiapit with Brigadier Kenneth Eather's 25th Infantry Brigade rather than displacing it forward as originally intended.
Dougherty flew over the area in a Douglas SBD Dauntless, and concurred with Vasey's assessment of the ground, although not with his appreciation of the enemy's intent.
Lieutenant Colonel F. H. Sublet's  2/16th Infantry Battalion, a unit from Western Australia, arrived at Kaiapit on 22 September. It set out at 15:00 that afternoon, crossing the Maniang River, which had a series of channels, extending across 2,000 yards (1,800 m). Its patrols attempted to locate the Japanese, as did aircraft from No. 4 Squadron RAAF. Only one saw any, the 12 Platoon, under Lieutenant J. R. Walder, which spotted three Japanese soldiers on the far side of the Umi River who fled when fired upon. Wallder's 12 Platoon, and 17 Platoon under Captain K. McCullough, crossed the Umi, which was about 50 yards (46 m) wide, up to 5 feet 6 inches (1.68 m) deep at the crossing point, and swift-flowing, and headed for Sagerak.
The 2/27th Infantry Battalion, a South Australian unit under the command of Lieutenant Colonel J. A. Bishop, arrived at Kaiapit on the morning of 23 September, having flown directly from Jacksons and Wards at Port Moresby in 45 USAAF C-47 transport aircraft, escorted by P-47 Thunderbolt, P-38 Lightning and P-39 Airacobra fighters. The first C-47 arrived at Kaiapit at 09:00 and the last at 10:50. Each took about ten minutes to unload all its troops and stores. The 2/27th took over the defence of Kaiapit from the 2/6th Independent Company. No aircraft arrived on 24 September, leaving Dougherty without the 2/14th Infantry Battalion, which was still back at Nadzab, and with only the rations and ammunition that the 2/16th and 2/27th had brought with them.
The pioneer platoon of the 2/16th strung a rope across the Umi River, allowing the heavily equipped diggers of B and C Companies to cross the fast-flowing torrent. They were across by 12:30, but the entire 2/16th did not complete the crossing until 20:00. On the other side, contact was made with Japanese units, and 12 Platoon came under light machine gun fire, but drove the Japanese off with its 2-inch mortars. When 17 Platoon was engaged by light machine guns, it used its 2-inch mortars to lay smoke, allowing it to withdraw. By 14:40, the leading platoon, 10 Platoon under Lieutenant W. J. Duncan, was overlooking Sagerak, but Duncan was wounded by a sniper at 17:00. Sublet ordered B Company to halt on the high ground, with the intent of attacking Sagerak the next day.
At 20:30, just a half-hour after it had completed the crossing of the Umi, the 2/16th received orders from Dougherty to pull back. With considerable lack of enthusiasm, the 2/16th re-crossed the Umi, this time in the dark. Re-crossing commenced at 03:00 and was completed by 08:00. Lieutenant R. G. Crombie's 11 Platoon was left behind on the high ground overlooking Sagerak. It entered Sagerak that morning, and found it deserted. About 16 Japanese soldiers fled when upon their approach, leaving behind their documents, medical stores and equipment. Lieutenant Everette E. Frazier, an American aviation engineer, pegged out a landing strip nearby and had it ready to receive C-47s in four hours.
Vasey flew into Kaiapit to talk to Dougherty. He explained that the reason for halting the 2/16th was an appreciation that Adachi would persist with his original plan, known to the Australians through documents captured at Kaiapit, even though it had been overtaken by events. Vasey believed that the open area between the Umi and Kaiapit would be an excellent place to destroy the Japanese force, should it choose to attack. He therefore proposed to halt for a while, reinforcing the position at Kaiapit with Brigadier Kenneth Eather's 25th Infantry Brigade rather than displacing it forward as originally intended. Dougherty flew over the area in a Douglas SBD Dauntless, and concurred with Vasey's assessment of the ground, although not with his appreciation of the enemy's intent.
Battle of Dumpu