The battle of the Driniumor River (10 July -25 August 1944) was a rare large scale Japanese counterattack on New Guinea and saw troops sent west from Wewak attack the American lines east of Aitape, achieving some early successes before being repulsed with heavy losses.
On 22 April 1944 American troops landed at Hollandia and Aitape (Operation Reckless), two major Japanese bases on the north coast of New Guinea. This move leapfrogged the strong Japanese positions further east at Wewak and Hansa Bay, now defended by most of General Adachi's 18th Army. Hollandia and Aitape fell within a few days and the Americans began work on turning Hollandia in a major base.
General Adachi still had 55,000 men at his disposal, and was determined to try and disrupt the American advance. He decided to send 20,000 men west, across 100 miles of jungle, to attack Aitape, in the hope that this would at least delay any further advances. An initial plan to attack Hollandia as well was abandoned after Adachi realised that his resources wouldn't allow it. Another 15,000 men were allocated to the logistical support of the attack, which would require most supplies to be carried by hand through the jungle. Adachi still had a few coastal barges at his disposal, but any attempt to use them attracted American attention. The attack force was trained in jungle survival skills before they set off.
The Aitape area was defended by the 32nd Division, commanded by Major-General Gill. When it became clear that the Japanese were planning to attack XI Corps HQ (General Charles P. Hall) took over at Aitape. The 112th Cavalry Regiment was moved to the area, as was the 124th Regimental Combat Team from the 31st Division. The 43rd Division was also prepared to move to the area. Hall had fifteen infantry battalions and two dismounted cavalry squadrons at the start of the battle. General Hall was under orders to break the momentum of the Japanese attack, and then counterattack once his force was strong enough.
The Americans had extended their beachhead for about thirty miles to the east of Aitape, eventually reaching beyond Dandriwad River. Ever since the original landings they had been expected to encounter Japanese forces in that direction, so Adachi's overall plan wasn't a surprise. At first American intelligence believed that the westwards moves they were detecting were either part of an attempt to protect the western flanks of the Eighteenth Army or to prepare for an attempt to bypass Aitape and Hollandia during a retreat to the west. Finally, in mid June, the Americans realised that an attack was likely. By the end of June they knew that parts of the 20th and 41st Divisions were on the Dandriwad.
Adachi's advance forces reached the American outposts east of the Dandriwad at the end of May, but they then had to pause to allow the main force to catch up. This delay meant that attack failed in its main objective, for on 17 May the first American troops landed on the mainland near Wakde Island, 125 miles to the west of Hollandia, as part of efforts to secure the rest of the north coast of New Guinea. The Japanese were able to force the Americans to pull back to the Driniumor River, twelve miles outside the Aitape perimeter, and this would be where the main battle was fought. The river was defended by three battalions and two cavalry squadrons, under General Clarence A. Martin. The Japanese had managed to get three regiments to the river by 10 July.
By the evening of 10 July the two sides were deployed along the Driniumor. On the Japanese side the 237th Infantry Regiment of the 41st Division was nearest the coast, with the 80th Regiment of the 20th Division next in line and the 78th Regiment of the 20th Division on the Japanese left.
The Americans covered a wider area. The 2nd Battalion, 128th Infantry, was nearest the coast, facing all three Japanese regiments. Next in line was the 3rd Battalion, 128th Infantry, and to their south was the 112th Cavalry. The American troops had more units along the coast to the west of the river. The forces on the American eastern flank were designated as the Persecution Covering Force.
The first major Japanese attack came on the night of 10-11 July, almost exactly when the original American intelligence reports had suggested, although the Persecution Force intelligence reports of 10 July hadn't predicted an immediate attack. Much to the American's surprise, Adachi had managed to move 70mm and 75mm artillery up to the front, and the attack began with an artillery bombardment followed by a fierce infantry attack. The artillery opened fire at 23.50 on the night of 10 July, hitting the 2nd Battalion, 128th Infantry, and firing for five minutes. The infantry attack followed immediately. The 78th Infantry was first to attack, soon followed by the 80th Infantry.
The 78th Infantry attack was repulsed by G Company, 128th Infantry, but the 80th and 237th Infantry made more progress. E Company was forced to retreat north-west by a lack of ammo, and by 3am the Japanese had punched a 1,300 yard wide hole in the American lines. By dawn on 11 July the two Japanese regiments were across the river.
This cut the American line in half. General Martin recalled the units that had been patrolling east of the river, and attempted to launch a counterattack to restore his original line. This attack failed, and the general decided to withdraw to his Second Delaying Position, on the Koronal Creek and X-ray River, three miles to the west. This decision wasn't appreciated further up the command chain, and General Krueger quickly ordered a counterattack.
Although the Japanese had achieved a great deal just by moving intact through the jungle from Wewak, their supplies were limited and communications were poor. Adachi was unable to take immediate advantage of his successes, and the new American line was left alone on the crucial night of 11-12 July, when a determined Japanese attack might have achieved more successes.
The Persecution Covering Force was reinforced with most of the 124th Infantry Regiment, and General Gill, commander of the 32nd Division, took over from General Martin. The counterattack began on 13 July, and the Americans soon regained their original positions. One Japanese force held out near the coast until the night of 16-17 July when it was destroyed while attempting to launch a counterattack of its own. Elsewhere the Americans had to cope with gaps in their line and isolated Japanese parties west of the river, but the situation had been stabilised.
Adachi's second major attack came at the end of July. This time his target was the village of Afua, at the southern end of the line. The Japanese were able to take the village on several occasions, but not to hang onto it. The village was first captured on the night of 21-22 July, after a series of attacks. The heavy fighting in this area worried the Americans, but also concerned General Adachi, who saw his overall plan being held up by the heavy fighting at the southern end of the line. On 25 July he ordered the 41st Division to move south to support the 20th at Afua, weakening the centre of his line. The Japanese launched a final heavy attack on the Afua front on 1 August, but this was repulsed with heavy losses. The final attack on this front came on 4 August, and was mainly intended to cover a Japanese retreat.
Further up the line the Americans were reinforced again, and were able to go back onto the offensive on 31 July. They managed to get behind the Japanese defenders of the river line, trapping many of them. By the end of 31 July the Americans had advanced some way east on two fronts, one near the coast and one in the centre of the Japanese lines. On 3 August they turned south, and by 5 August were east of the Japanese fighting at Afua. They then turned west, and applied pressure on that force. On 9 August Adachi finally gave up and ordered a retreat back to Wewak. The Americans launched a counterattack that forced the Japanese back to the Dandriwad, where a Japanese rearguard held them up. The Americans then pressed the retreating Japanese for a few weeks, but eventually let them continue on their way. The battle for the Driniumor was officially judged to have ended on 25 August.
The attack on the Driniumor had been costly for the Japanese, who had lost between 8,800 and 10,000 dead between 22 April and 25 August. This period includes the initial attack on Aitape, but resistance had been light, so most of the casualties came during the Driniumor counterattack. The Americans had lost 440 dead and 2,500 wounded, but they had fought off the last serious challenge to their position on New Guinea. The battle destroyed any attacking potential left within the three Japanese divisions involved, and forced Adachi to go entirely onto the defensive. Adachi was left largely alone until the Australians took over at Aitapi and decided to attack him at Wewak. He was eventually forced into the mountains, and didn't finally surrender until September 1945.