The battle of Dumpu (8-13 December 1943) was a rare Japanese counterattack during the fighting in the Finisterre Range on New Guinea, and saw them attempt to push the Australians out of their furthest outposts downstream from Dumpu in the Ramu Valley.
After capturing Lae and Salamaua on the Huon Gulf the Australians sent their 7th Division up the Markham Valley and over the watershed into the western flowing Ramu Valley. They captured Dumpu, where by the end of November there were two active airstrips, and then focused their attention on the area to the north. The Japanese had been building a road across the mountains from the north coast in an attempt to link their base at Madang with Lae and Salamaua, and this route approached Dumpu from the north. If it had been completed then it would have come over the Kankiryo Saddle and down the Faria River towards Dumpu (passing alongside the famous 'Shaggy Ridge', which bordered the river to the west). The main Australian efforts thus went into securing the southern end of this potentially dangerous route.
They also had to guard the north-western approaches to Dumpu up the Ramu Valley. In early December furthest major outposts north of the river were held by part of the excellent Papuan Infantry Brigade and the 2/6th Commando Squadron, in the area of Kesawai and the nearby foothills.
Early in November Australian patrols in the area west of these positions reported an increase in Japanese activity. There was also some evidence that the main road had been in use in the previous days. The Japanese had two routes into the area - one was to use the road to its upper reaches then cut south across the mountains. The other was to swing around the north-western end of the mountains and come up the Ramu Valley. The attack was carried out by the 1/78th Regiment and parts of the 239th Regiment. The Japanese aims appear to have been limited to pushing the Australians out of their further outposts.
The Japanese attack began early on 8 December. The Papuan outposts were soon forced to retreat south-east to the Evapia River. The Japanese soon set about digging in just above Kesawai, where they could cut the links to the Australian outposts further down the valley. This left part of the 2/6th Squadron cut off. The Australians reacted to the attack by moving two companies from the 2/25th Battalion forward to the Evapia, and preparing for a possible major attack. General Vasey attempted to get the 18th Brigade as reinforcements, but this request was turned down.
On 9 December the Japanese attacked the isolated Australian positions at Ketoba and Isariba, to the north-west of Kesawai. The Australians were forced out of Ketoba, but held on to Isariba. The Japanese made five attacks on this isolated position. During the fourth the isolated post finally received orders to withdraw behind the Evapia. At 4.15pm they abandoned Isariba, moved south to the Ramu then moved up the river towards the rest of their unit, by now forming up on the Mene River, to the south-east of the Evapia. The same day saw the two companies from the 2/25th reach the Evapia and then dug in some way to the north-west of the river.
10 December and 11 December were quite quiet. The Australians patrolled from the Evapia, while the Japanese carried out a minor bayonet attack on Shaggy Ridge. Elsewhere the isolated Australian forces continued to return to the safety of their own lines. On 12 December there were clashes between Australian patrols and the Japanese.
The Japanese launched a major attack an hour after midnight on the night of 12-13 December, hitting Cox's Company of the 2/25th, on the Australian right. The Japanese attack ran into heavy fire, including three Bren guns and a Vickers gun. Despite having machine gun support of their own the Japanese attack was repulsed without making any progress. If the Japanese had planned to attack Robertson's Company, on the Australian left, this attack was dispersed by a grenade attack before it began. These early setbacks didn't discourage the Japanese, who appeared to have around 400-500 men, and the two Australian companies had to fight off four and a half hours of repeated attacks. Artillery support was intermittent, with broken communications causing most of the problems, and ammo was limited, but the Japanese were unable to make progress.
The Australians were worried that their positions would be badly exposed to machine gun fire after dawn. Robertson ordered his men to prepare for a possible withdrawal, and at the same time to move into the trees on the western edge of his position. The brought them very close to the Japanese. Both companies were now in a vulnerable position, and so just before dawn Robertson ordered both companies to pull back to a reserve position about a mile to the rear. The retreat began at 5.30am, and the two companies united in their new position just after 7.30am.
The Japanese didn’t follow up. They had suffered heavy losses during the night attack, and were now subjected to a heavy artillery bombardment. A patrol on 14 December found the battlefield abandoned, but air patrols on 13 December found signs of a sizable Japanese presence in the general area. In order to close gaps in his lines Brigadier Eather decided to pull Robertson and Cox back another two miles, to the east bank of the Evapia River. At the same time General Vasey, the divisional commander, decided to base his main defensive line on the Yogia River, a little nearer Dumpu than the Evapia. Plans were put in place to cope with a major Japanese attack, but this never came. Instead the Australians were soon able to return to the areas lost on 8 December, and the Japanese quickly withdrew back to their starting point. The main focus of attention then returned to the Shaggy Ridge area.