Navigational errors resulted in the troops being landed on the wrong beach, with some of them coming ashore at Siki Cove and taking heavy fire from the strong Japanese defences in pillboxes.

The Japanese had established strong defences along the river's southern bank, which the Australians attempted to outflank by sending a force to the west, climbing through steep terrain.

Despite taking casualties, the Australians were able to establish themselves south of the Bumi and at that point the 2/13th Infantry Battalion began to advance on Finschhafen from the west.

[2] The bombing of Wewak, in which 100 Japanese aircraft were lost in August 1943, caused Imperial General Headquarters (IGHQ) in Tokyo to reconsider whether Eastern New Guinea and the Solomon Islands could be held.

Concluding that it could not, IGHQ authorised the commander of the Japanese Eighth Area Army to conduct a fighting withdrawal to a new defensive position in Western New Guinea, which it hoped would be ready in 1944.

To strengthen the defences there, Adachi ordered the 80th Infantry Regiment and a battalion of field artillery from the 20th Division at Madang to move to Finschhafen on 7 August 1943.

The main body, under Lieutenant General Shigeru Katagiri, left Bogadjim bound for Finschhafen on 10 September, but was not expected to arrive before October.

Apart from a thin, flat coastal strip, at the time of the campaign, the area was thickly covered with dense jungle, through which very few tracks had been cut.

Brigadier General Charles A. Willoughby, the Assistant Chief of Staff (G-2), and therefore the head of the intelligence branch at MacArthur's GHQ, considered Finschhafen to be primarily a transhipment point, and the troops there to be mainly from line of communication units.

[17] The intelligence staff at Blamey's Allied Land Forces Headquarters (LHQ), headed by Brigadier J. D. Rogers, had come up with a much higher figure of 3,000.

Rear Admiral Daniel E. Barbey, the commander of the VII Amphibious Force, had originally counted on four weeks break between the fall of Lae and the Finschhafen operation.

[22] As at Lae, the first wave, consisting of two companies each from the 2/13th and 2/7th Infantry Battalions, would land in plywood LCP(R)s launched by the four destroyer transports,[26] the USS Brooks, Gilmer, Humphreys, and Sands.

[27] The remainder of the assault would land in six LSTs, 15 LCIs, and six LCTs of the VII Amphibious Force, and 10 LCMs and 15 LCVPs of the 532nd Engineer Boat and Shore Regiment.

[34] Barbey and the Commander of Allied Naval Forces, Vice Admiral Arthur S. Carpender, did not want a repeat of what happened at Lae,[35] when two LCIs were lost and two LSTs were badly damaged.

Noting that it was the rainy season, and the sky would therefore likely be overcast, Herring doubted that the VII Amphibious Force would be able to locate the beach, and pressed for a dawn landing at 05:15.

[35] Samuel Eliot Morison, the US Naval historian, noted that: "The Australians proved to be right; 'Uncle Dan's' outfit was not prepared for a neat night landing.

While they were en route during the night, a Japanese raid on Buna sank an LCS(S), and damaged a dock and two merchant ships; nine people were killed and 27 wounded.

[44] Scarlet Beach and Siki Cove were covered by bunker-type pillboxes made of logs, spaced about 50 yards (46 m) apart, and connected by shallow trenches.

With the help of an American Amphibian Scout, Lieutenant Herman A. Koeln, Huggett attacked the posts with grenades and small arms.

A Japanese soldier threw a hand grenade at them that killed one man and wounded the brigade intelligence officer, Captain Barton Maughan.

They arrived over the Finschhafen area after dark at 19:15, where a drop zone in a Kunai patch was marked by men holding hand torches.

[72] As one of his final actions before returning to LHQ in Brisbane, Blamey instructed Herring to arrange for the reinforcement of Finschhafen with an extra brigade and 9th Division Headquarters.

[73] That day, though, MacArthur, who also returned to Brisbane on 24 September,[74] had issued an instruction that operations at Finschhafen were "to be so conducted as to avoid commitment of amphibious means beyond those allotted".

[76] MacArthur feared that committing additional resources would tie them up, and perhaps result in losses, that would delay upcoming operations, relinquishing the initiative to the Japanese.

[81] It was arranged that the first LST departing Lae on the night of 28/29 September would stop at G Beach and collect the 2/43rd Infantry Battalion and a platoon of the 2/13th Field Company, a total of 838 men.

[91][65] Grace ordered Major Ron Suthers to outflank the Japanese position by moving through the foothills of the Kreutberg Range, as previously instructed by Windeyer.

[89][90] A large Japanese air raid at 12:30 by 20 fighters and 12 bombers struck the Australian positions around Launch Jetty and the Finschhafen airstrip.

[101] Sergeant G. R. Crawford led 11 and 12 Platoons of the 2/13th Infantry Battalion in a bayonet charge on the Japanese positions covering Ilebbe Creek.

[109][110] It had been intended that once the beachhead was overwhelmed, that the 79th and 80th Infantry Regiments would link up and then clear the Finschhafen and Langemark Bay areas; but the assault was poorly co-ordinated and failed to achieve sufficient weight to overcome the Australians, while also suffering from a lack of artillery.

The seaborne assault was interdicted by US Navy PT boats, which inflicted heavy casualties, and was destroyed by Allied machine gunners on the beach.