The river is approximately east of Aitape. The landings at several key points around Hollandia on 22 April had cut off the Japanese 18th Army, which was retreating westwards toward the Japanese Second Area Army in Dutch New Guinea. U.S. troops landed and seized Aitape on 22 April, after which the 163rd Regimental Combat Team consolidated their positions. In early May, the 32nd Infantry Division replaced the 163rd, and a defensive perimeter was established around the airfields in the area, and U.S. troops undertook patrols to locate the Japanese troops in the area. These troops were centered around Wewak, about from Aitape. The Japanese 18th Army—which had not been reinforced after severe losses in the Lae, Huon Peninsula and Finisterre Range campaigns—was commanded by Lieutenant-General Hatazō Adachi. Consisting of 20,000 troops, its main fighting units were the 20th and the 41st Divisions. Intelligence derived from codebreaking as well as captured documents and Allied Intelligence Bureau patrols, other sources indicated that the Japanese 18th Army was approaching the Driniumor with the intention of breaking through and retaking Aitape. As early as late May, General Walter Krueger had ordered reinforcements into the area. In late June, the Allies began moving the 43rd Infantry Division from New Zealand, and the 112th Cavalry Regiment and 124th Infantry Regiment arrived from eastern New Guinea. By late June, Allied forces in the area had been built up to corps strength, and XI Corps commander, Major General Charles P. Hall had established his headquarters at Aitape. Around this time, a covering force comprising the 112th Cavalry Regiment was sent approximately 20 mi east to guard Aitape's eastern flank on the line of Driniumor River. Despite these preparations, the Allied intelligence picture was confusing and contradictory and in the lead up to the attack, Allied patrols were unable to locate the Japanese troop concentrations throughout early July, with the result that the initial Japanese assault caught the defenders by surprise.
Battle
On the night of 10/11 July, an assault force of perhaps 10,000 Japanese attacked en masse across the Driniumor. Despite suffering appalling casualties from machine guns and artillery, the Japanese pressed on and forced a major breach in the American line. Ed Wanat, a veteran of this battle, stated that the Japanese bodies had piled up in front of their machine gun so high that they could not fire over them. They had to leave their fox holes and pull bodies out of the line of fire so that they had a clear line of fire upon the enemy. This occurred during the numerous Japanese attacks. After a harrowing fighting withdrawal through the jungle that night, the defenders managed to regroup where possible and by the 13th were counterattacking to try to seal the breach. Valuable fire support was provided by Australian and U.S. fighter bombers, and by Task Force 74, comprising two Australian cruisers, two Australian destroyers and two U.S. destroyers. Allied PT boats and destroyers also interdicted Japanese barge supply convoys between Aitape an Wewak and fired upon troop concentrations along coastal avenues of advance. The 32nd Infantry Division experienced the heaviest attacks, although the 112th Cavalry and 124th Infantry from the 43rd Infantry Division were also heavily engaged. The remainder of July saw heavy fighting west of the river as platoon and company sized units clashed in the jungle. Heavy pressure was maintained upon some pockets of American troops still clinging to their positions at the river as they became encircled by Japanese troops, determined on wiping them out. By the beginning of August, however, the Japanese drive was spent and they were flung back over the Driniumor. By 4 August, Adachi ordered a complete withdrawal, although fighting lasted until around 10 August as U.S. troops continued their annihilation of the Japanese force. The remnants retreated further east to Wewak and the battle was officially declared over on 25 August.
Aftermath
Four U.S. soldiers were awarded the Medal of Honor, for acts of outstanding valor during the battle; Private Donald R. Lobaugh and Staff Sergeant Gerald L. Endl of 32nd Division, and Second Lieutenants George W. G. Boyce, Jr. and Dale Eldon Christensen of 112th Cavalry Regiment. All told the Americans suffered almost 3,000 casualties including 440 killed and 2550 wounded and 10 missing, while the Japanese lost 8,000–10,000 men. The four-week Battle of Driniumor River was one of the costliest of the campaigns in Papua and New Guinea, second only to the bloody head-on Allied assaults of the Japanese strongholds at Gona, Buna and Sanananda from November 1942 – January 1943.
