The Battle of Driniumor River, also known as The Battle of Aitape, 10 July – 25 August 1944, was part of the Western New Guinea campaign of World War II. Japanese forces attacked United States forces on the Driniumor River, near Aitape in New Guinea. The battle should not be confused with Operation Persecution, which included amphibious landings near Aitape in April 1944, or the Aitape-Wewak campaign, which began in November. The Japanese referred to the Driniumor as the Hanto.
The river is approximately 20 mi (32 km) 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. When U.S. troops landed and seized Aitape on 22 April, a covering force comprising the 32nd Infantry Division and 112th Cavalry Regiment was sent approximately 20 mi east to guard Aitape's eastern flank on the line of Driniumor River. The 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. Its main fighting units were the 20th and the 41st Divisions.
Ultra intelligence derived from codebreaking as well as other sources indicated that the Japanese 18th Army was approaching the Driniumor with 20,000 troops with the intention of breaking through and retaking Aitape. Unfortunately, the Allied intelligence picture was confusing and contradictory, with the result that the initial Japanese assault caught the defenders by surprise.
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 (TF 74), comprising two Australian cruisers and two U.S. destroyers.
The remainder of July saw heavy fighting west of the river as platoon and company size 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.
Four U.S. soldiers were awarded the Medal of Honor (all posthumously), 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 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.