The Battle of the Pimple was part of the Markham and Ramu Valley – Finisterre Range campaign, which consisted of a number of battles fought by Australian and Japanese troops in Papua New Guinea in World War II. Fought on 27 and 28 December 1943, the battle took place as the Australians advanced towards the Japanese strong hold around Shaggy Ridge, and was a preliminary phase in their eventual capture of that position in January 1944. Supported by artillery, mortars, machine guns and fighter-bomber aircraft, the assault was made across a narrow frontage, which was usually not much wider than a single section. Two companies of Australian infantry were committed to the attack, with one securing the initial crest, while the other exploited the position and secured several other smaller features throughout the two days of fighting. In the aftermath, Japanese artillery harassed the Australians holding the position, and subjected them to several counter-attacks, which were eventually defeated.
Background
After hard fighting in the Pacific throughout 1942, the following year Australian and US forces began to gain momentum against the Japanese, and were contemplating going on the offensive. In New Guinea, the bloody Battle of Buna–Gona had been fought to a conclusion in January, while a Japanese attempt to secure the vital airfield at Wau, near Salamaua, had also been repelled that month. Throughout mid-1943, the Australians had fought a campaign against the Japanese in the Salamaua region, as they had advanced east from Wau towards the Huon Gulf. In September, an amphibious landing near Lae was carried out in conjunction with an airborne assault on Nadzab, aimed at capturing Lae. At the same time, Australian troops, who had been reinforced by several US battalions, continued to keep up the pressure around Salamaua, which fell in mid-September around the same time as Lae. As the Allies sought to follow up the large number of Japanese troops that managed to withdraw from Lae, they subsequently launched the Huon Peninsula campaign.
After the 9th Division had secured Finschhafen and Sattelberg, the next major objective in New Guinea was to capture Shaggy Ridge in the Finisterre Ranges, a series of high positions held by Japanese infantry, supported with some artillery. This task was allocated to the Major General George Vasey's 7th Division, which had – after the capture of Lae – advanced to Dumpu before beginning an advance through the Markham and Ramu Valleys towards the Finisterre Ranges. In October, the 21st Infantry Brigade began a tentative push towards the foothills surrounding Shaggy Ridge, and in the middle of the month fought a sharp defensive action around John's Knoll and Trevor's Ridge after the Japanese counter-attacked an Australian force that had cut the main Japanese line of supply.
Battle
Shortly after the fighting around John's Knoll, the 25th Infantry Brigade had relieved the 21st and had begun patrolling the area, while aerial reconnaissance attempted to locate the Japanese artillery, which was engaged by the guns of the 2/4th Field Regiment. Throughout the previous months, the Japanese had largely sought to avoid contact, but after several months Allied reconnaissance began detect a build up of Japanese troops. By early December, the Japanese began sending reinforcements south of Bogadjim through Saipa and Orgorunna. In response, the Australians began planning their own offensive to secure Shaggy Ridge, and the 21st Infantry Brigade subsequently took over from the 25th once again.
In order to assault Shaggy Ridge and the Kankiryo Saddle, the Australian 7th Division had to secure a foothold on the southern slope of the ridge around a position dubbed "The Pimple", which was one of three rocky outcrops, held by the Japanese on the ridge line. The Japanese troops defending the area were drawn from 2nd and 3rd Battalions of the 78th Infantry Regiment, which formed part of the Nakai Detachment under the command of Major General Masutaro Nakai, who was subordinated to the 18th Army. Australian estimates of the strength of these forces around the Pimple placed them at around three platoons. For two months the Pimple held up the Australian advance; and attempts by the Australians to find a way around the position had been thwarted. Australian commanders subsequently decided that a direct attack would be required in order to deny the Japanese the use of the position for observation purposes.