The Landing at Scarlet Beach (Operation Diminish) took place in New Guinea in September 1943, during the Huon Peninsula campaign of the Second World War. Allied forces landed at Scarlet Beach, north of Siki Cove and south of the Song River, to the east of Katika and about north of Finschhafen. The capture of Finschhafen allowed the construction of air bases and naval facilities to assist Allied forces to conduct operations against Japanese bases in New Guinea and New Britain.
After Lae had fallen sooner than the Allies had anticipated, they exploited the advantage. As a result of faulty intelligence, which underestimated the size of the Japanese force in the area, the assault force chosen consisted of only Brigadier Victor Windeyer's 20th Infantry Brigade. The landing at Scarlet Beach that took place on 22 September 1943 was the first opposed amphibious landing that Australian forces had made since the Landing at Anzac Cove in the Gallipoli Campaign of 1915. 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. After re-organising, the Australians pushed inland. The Japanese put up stiff resistance on the high ground at Katika, but were forced back. By the end of the day, the Australians had secured their objectives. The Japanese launched a retaliatory air raid on the ships of the VII Amphibious Force, but US fighter aircraft defended the convoy and no ships were hit. Continued Japanese air attacks on the beachhead inflicted numerous casualties over the course of the battle.
The next day the Australians commenced their advance south towards the village of Finschhafen, about south of the landing beach, with the 2/15th Infantry Battalion leading the way to the Bumi River. 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. Once they had located a suitable place to cross the river, they began wading across but were fired upon by a group of Japanese naval infantry who were positioned on a high feature overlooking the river. Despite taking casualties, the Australians were able to establish themselves south of the Bumi River and at that point the 2/13th Infantry Battalion began to advance on Finschhafen from the west. Meanwhile, the 2/15th attacked the left flank of the Japanese that had opposed their crossing. After advancing up the steep slope under fire, sometimes on their hands and knees, the 2/15th took the position at the point of the bayonet, killing 52 Japanese in close combat.
Australian fears of a Japanese counter-attack grew and they requested reinforcements from General Douglas MacArthur. This was denied as his intelligence staff believed there were only 350 Japanese in the vicinity; in fact, there were already 5,000. The Australians received some reinforcements in the shape of the 2/43rd Infantry Battalion. The arrival of this unit meant the entire 20th Infantry Brigade could concentrate on Finschhafen. The Japanese naval troops which were holding Finschhafen began to withdraw and Finschhafen fell to the Australians on 2 October. The 20th Infantry Brigade then linked up with the 22nd Infantry Battalion, a Militia infantry battalion that had cleared the coastal area in the south of the Huon Peninsula, advancing from Lae over the mountains. The Japanese withdrew into the mountains around Sattelberg.
Strategy Allied
At the Pacific Military Conference in Washington, D.C., in March 1943, the Joint Chiefs of Staff approved plans by General Douglas MacArthur, the Supreme Commander, South West Pacific Area (SWPA), for an advance on the Japanese base at Rabaul. On 13 June 1943, MacArthur's General Headquarters (GHQ) in Brisbane instructed General Sir Thomas Blamey's New Guinea Force to
Following the successful seaborne landing at Lae and airborne landing at Nadzab, Salamaua, Lae, and the Markham River Valley were all in Allied hands by 16 September 1943. Blamey then turned his attention to his next objective: Finschhafen.
Japanese 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.
Lieutenant General Hatazō Adachi, the commander of the Japanese XVIII Army in New Guinea, recognised the importance of the Finschhafen area, and had placed Major General Eizo Yamada, the commander of the 1st Shipping Group, in charge of defending it. 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 headquarters, artillery, and heavy weapons departed Bogadjim on 15 August and travelled by sea, but the remainder marched along the coast.
On 26 August, Adachi assigned the 2nd Battalion, 238th Infantry Regiment, part of the 41st Division, which was in the area en route to join the rest of the 238th Infantry Regiment at Salamaua, to remain in the Finschhafen area under Yamada's command. The landing at Lae on 4 September made an Australian advance on Finschhafen appear imminent, and Adachi ordered the rest of the 20th Division, less the Nakai detachment in the Markham Valley, to move to Finschhafen. The main body, under Lieutenant General Shigeru Katagiri, left Bogadjim bound for Finschhafen on 10 September, but was not expected to arrive before October. In the event of an Allied attack before he arrived, Yamada was to hold the high ground around Sattelberg and prepare for a counter-attack.
Geography The Huon Peninsula is situated along the north-east coast of Papua New Guinea, and stretches from Lae in the south on the Huon Gulf to Sio in the north along the Vitiaz Strait. Along the coast, between these two points, numerous rivers and streams cut the terrain. Of these, the most prominent are the Song, Bumi, and Mape Rivers. These waterways flow from the mountainous interior, which is formed through the conglomeration of the Rawlinson Range in the south with the Cromwell Mountains in the east. These meet in the centre of the peninsula to form the Saruwaged Range massif, which joins the Finisterre Range further west. 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.
During planning, the Allies identified three areas as key and decisive terrain in the area: the beach north of Katika, which was later codenamed "Scarlet" by the Allies, the peak called Sattelberg to the south west, which dominated the area due to its height, and Finschhafen, possessing a small airfield and sitting on the coast in a bay which offered protected harbour facilities. Before the war, the town had a population of about 30 white and 60 indigenous people. There were good anchorages for vessels of up to 5,000 tons in Dreger Harbour, Langemak Bay, and Finsch Harbour. The flat coastal strip provided a number of potential airfield sites. German names abounded in the area because the Territory of New Guinea was a German colony from 1884 until it was occupied by Australia in 1914.
Prelude Intelligence Allied estimates of the number of Japanese troops in the Finschhafen area varied. 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. The fall of Lae ended its utility, so he reduced his estimate of the number of Japanese troops in the area from 500 to 800 to just 350. Based on this appreciation, GHQ believed Finschhafen would be a "pushover".
There was reason to believe otherwise. A ten-man Allied Intelligence Bureau patrol that included three Australian officers, an American amphibian scout from the US Army's 532nd Engineer Boat and Shore Regiment, a signaller from Z Special Unit, and several Papua New Guinea soldiers, was landed during the night of 11/12 September in rubber boats launched from two PT boats. The scouts were unable to obtain the hydrographic information they sought due to Japanese patrols in the area. A number of machine-gun nests were identified during their reconnaissance of the enemy positions before they were extracted on 14 September.
As had happened during the Kokoda Track campaign and the Battle of Buna–Gona, estimates by Australian intelligence differed greatly from those at GHQ, as they used different methods. 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. I Corps produced an estimate of 1,800, which was passed on to the 9th Division along with GHQ's estimate, which it rejected. The Allies' best source of intelligence, Ultra, shone no light on the matter. Finschhafen was mentioned in only five decrypted messages in the previous three months, and most of these were in the insecure Japanese Water Transport Code. Only after the capture of Japanese codebooks in the Battle of Sio in January 1944 were the Allies able to systematically break into the Japanese Army codes. In fact, Japanese strength in the area on 22 September was about 5,000.
Planning Two contingency plans were prepared by Lieutenant General Sir Edmund Herring's I Corps. One was a ship-to-shore operation by the 6th Division's 16th Infantry Brigade or the 7th Infantry Brigade, a Militia formation at Milne Bay; the other was for a shore-to-shore operation by a brigade of Major General George Wootten's 9th Division. The operation was codenamed "Diminish", which was actually that of Finschhafen itself. In the plan produced by I Corps on 24 August 1943, Herring selected beaches immediately south of the Song River for the landing. Indications were that it was suitable for landing craft. Most of the Japanese defenders and defences were believed to be facing south in anticipation of an Australian overland advance from Lae. It avoided having to cross the Mape River, which was believed to be a significant obstacle. The landing beach became known as Scarlet Beach from the post-landing red screens and lights used to guide landing craft. The left end of the beach was marked with a solid red panel mounted on tent poles, the right with one alternating red and white. At night, the left would have a red light, and the right one alternating red and white. This scheme was first used at Red Beach during the landing at Lae. To avoid confusion of having two Red Beaches, the landing beach was called Scarlet Beach instead.