The Battle of the Driniumor River

Shortly before midnight on 10 July 1944, Japanese 70 mm and 75 mm mountain guns, dragged laboriously through the jungle, opened fire on American positions on the Driniumor River, some 30 kilometres east of Aitape on the north coast of New Guinea. According to the US official history, the shelling began at about 11.50 p.m., and a few minutes later, as the guns fell silent, the infantry started across the river; some accounts give an earlier time, 10.55 p.m. About 10,000 men of General Hatazō Adachi’s Japanese 18th Army attacked in waves against a sector held by two companies of the US 32nd Infantry Division. Before dawn on 11 July the Driniumor line had been broken. So began the battle that the Americans also called the Battle of Aitape – one of the bloodiest of the entire New Guinea campaign.

War chronologies record under this date only that “the Japanese are still resisting in New Guinea”. That is true, but by July 1944 it was no longer merely a matter of resistance. Instead of defending itself at Wewak or breaking out to the west, Adachi’s cut-off army went over to the attack against an American base, and it was on the night of 10–11 July that the attack began.

A cut-off army

In the spring of 1944 the Japanese 18th Army – three exhausted divisions, the 20th, 41st and 51st, with some 55,000 men between them – was falling back along the north coast of the island towards Wewak. Behind it lay lost campaigns on the Huon Peninsula and in the Finisterre Range, in which it had lost most of its heavy equipment. On 22 April 1944 General Douglas MacArthur leapfrogged it in a single move: the Americans landed at Hollandia and Aitape, hundreds of kilometres west of its positions. Adachi’s army was trapped in the eastern part of the island, between the Americans to the west and the Australians, who had taken Madang at the end of April.

On 2 May Japanese Imperial General Headquarters ordered the 18th Army to bypass Hollandia and Aitape through the interior and join the 2nd Army in western New Guinea. Adachi was unwilling to comply. The retreat from the Huon Peninsula and the crossings of the Ramu and Sepik rivers had already cost him thousands of men; a march west through swamps and mountains, he believed, could destroy the army more thoroughly than a battle. Sitting idle at Wewak was not an option either: the terrain was suited neither to a long defence nor to cultivation, and supplies would last only until September. According to the American historian Robert Ross Smith, author of the official history volume on the campaign, Adachi concluded that the only way to obtain supplies, maintain morale and contribute to the war effort was to attack the Allied positions. The order to break through to the west was rescinded in mid-May, but the plan to attack Aitape had been drawn up at 18th Army headquarters as early as 26 April. At first Adachi even considered retaking Hollandia, but he soon limited his objective to Aitape and the Tadji airfields.

An offensive on half rations

The plan envisaged an attack by two divisions, the 20th and 41st, reinforced by the 66th Infantry Regiment of the 51st Division. On paper Adachi assembled some 20,000 men for the offensive, but – as Smith calculates from Japanese documents – no more than 8,000 of them were trained infantry. Some 2,500 were gunners, about 5,000 were to carry supplies behind the attacking units, and the rest were service, signals and staff personnel who were to fight as infantry if need be. A further 15,000 men carried supplies forward from Wewak towards the front. The remaining 20,000 or so stayed at Wewak – some as a garrison, others because they were too sick or exhausted to fight.

The Japanese built a road about 60 kilometres long westwards from Wewak, but American aircraft and PT boats stopped supply barges from getting through along the coast, and almost everything had to be carried on men’s backs through the jungle. The army had only half the ammunition that Japanese regulations prescribed for a major battle; for the mountain guns the shortage was critical. Signals equipment was running out, and there was a lack of mosquito nets, clothing and anti-malaria drugs. For months the soldiers had been on half rations; part of the 20th Division lived for a time on less than 300 grams of starchy food a day, and some forward units on nothing but starch from the sago palm. The date of the attack was postponed several times; on 19 June Adachi decided that the assault on the Driniumor line would come no earlier than 10 July.

On the other side of the river

Aitape was defended by a force named after the code name of the April landing, the Persecution Task Force. Its main task was to protect the Tadji airfields. From May the core of the defence was General William Gill’s 32nd Infantry Division, which had relieved the landing troops. General Walter Krueger, commander of the Sixth Army, knew from captured documents, patrol reports and radio intercepts that the 18th Army was preparing to attack, and from the end of May he sent reinforcements to Aitape: the 112th Cavalry Regiment – dismounted and numbering no more than 1,500 men – under Brigadier General Julian Cunningham, the 124th Infantry Regiment of the 31st Division, and later the 43rd Infantry Division, shipped in from New Zealand. On the night of 27–28 June command of the whole force passed to Major General Charles P. Hall, commander of XI Corps. On the river itself stood Brigadier General Clarence Martin’s covering force: three battalions of the 32nd Division and two cavalry squadrons, stretched along a front several kilometres long, from the coast to the village of Afua inland.

The Americans had an advantage of which the Japanese were unaware: decrypted Japanese Army signals, passed on through the “Ultra” system. These indicated that the attack was imminent. Yet, as the historian Edward Drea later showed, the same messages also revealed the 18th Army’s desperate supply situation, and MacArthur’s intelligence chief, Brigadier General Charles Willoughby, and General Hall leaned towards the conclusion that a starving army was incapable of a serious attack. Several times in late June and early July an alert was sounded and no attack came, because the Japanese had to keep postponing it. The intelligence was thus at once accurate and misleading.

Krueger wanted to seize the initiative from the Japanese and settle the Aitape question as quickly as possible, so as to free troops for further leaps westwards. On 8 July he ordered Hall to send a strong reconnaissance in force across the river. Martin protested, because the units would have to come from the already thin Driniumor line, but on the morning of 10 July the 1st Battalion of the 128th Infantry Regiment set off eastwards along the coast, and the 2nd Squadron of the 112th Cavalry inland from Afua. The defensive line had been weakened on the eve of the attack. That day patrols reported Japanese movements just beyond the river; one battalion commander put his men on alert, but the reports went no higher. The task force’s evening intelligence report spoke only of a possible preparation for an attack at some unspecified time in the future, and at about 11.30 p.m. Hall reported to Krueger that the reconnaissance could continue in the morning.

The night of 10–11 July

Less than half an hour after that report was sent, the first shells fell on the river. The attack was to go in simultaneously with three regiments – the 78th, 80th and 237th – side by side on the sector between the villages of Paup and Afua. In the darkness and dense jungle coordination failed: the 78th Regiment moved off earlier than the 80th, and the main body of the 237th reached the river only at around 2 a.m. The full weight of the blow fell on Companies E and G of the 2nd Battalion, 128th Infantry, supported by a second battalion of the 127th Regiment. American machine guns, mortars and the howitzers of two field artillery battalions, which had registered on the crossings in advance, cut down the attackers in whole groups. Yet the Japanese kept coming, wave after wave.

Company G for the most part held its positions. Company E in the centre of the line could not withstand the pressure: its organisation and communications broke down and its men began to run out of ammunition. Some withdrew north to the neighbouring company on the coast, some to the rear, and a few men hid among the Japanese for three days. According to Smith the company lost about 10 killed and 20 wounded; it was not casualties but the lack of ammunition and the disintegration of the unit that forced the withdrawal. A gap more than a kilometre wide opened in the Driniumor line, and before dawn more Japanese units poured through it, followed by gunners, medical orderlies and headquarters staff. At first light on 11 July the 78th and 80th Regiments were re-forming on high ground a few hundred metres behind the former American line.

General Martin did not know how large the gap was and had no reserve with which to close it. With Hall’s approval he recalled the reconnaissance units from the far bank – the 1st Battalion of the 128th received the order at 1.35 a.m. and was on the march by 2 a.m. – and decided to wait until daylight before attempting to retake the line. Over 11 and 12 July, however, the covering force fell back further, to a second delaying line on the X-ray River and Koronal Creek, a few kilometres to the west. The Japanese were unable to exploit their success: their units were intermingled and exhausted, communications were faltering, and the ammunition carried with such difficulty from Wewak was quickly running out.

Afua and the weeks that followed

The battle that began that night lasted more than another month. As early as 13 and 14 July the Americans counter-attacked, supported by two battalions of the 124th Infantry and the fire of several howitzer battalions, and restored the line on the river. The focus of the fighting shifted south, to the area of the village of Afua at the foot of the Torricelli Mountains. From mid-July units of the 20th Division repeatedly attacked the 112th Cavalry and the 127th Infantry there; Afua changed hands several times, and cut-off American groups held out in encirclement, supplied by airdrops. At the end of July Adachi threw in his last reserves – around 24 July the 66th Regiment crossed the river, and most of the 41st Division was then moved south. The offensive gained some ground, but at the cost of heavy losses. At the same time, from 31 July, the Americans launched a counter-stroke by units of the 124th and 169th Infantry Regiments eastwards across the Driniumor and into the Japanese rear, threatening to encircle the Japanese forces around Afua. On 4 August Adachi ordered a retreat towards Wewak; fighting with Japanese rearguards went on until about 9 August, and on 25 August Krueger declared the operation over.

From the sea the Americans were supported by a naval force including the Australian cruisers HMAS Australia and HMAS Shropshire, and from the air by Australian Beauforts and Beaufighters flying from Tadji airfield. PT boats and destroyers hunted Japanese barges moving along the coast from Wewak.

Other New Guinea fronts in July

The fighting on the Driniumor took place in the rear of a front that had long since moved west. On the island of Biak, where the Americans had landed on 27 May, the airfields were operating from the second half of June, but Japanese soldiers held out in caves throughout July and the last pockets of resistance were eliminated only in August. On 2 July, eight days before Adachi’s attack, General Edwin Patrick’s 158th Infantry Regiment landed on Noemfoor, an island lying between Biak and the Vogelkop (Bird’s Head) Peninsula. The Japanese offered almost no resistance on the beaches and withdrew inland, and on 3 and 4 July paratroopers of the 503rd Parachute Infantry Regiment were dropped onto Kamiri airfield, many of them injured on landing on the hard runway. Scattered Japanese were hunted down on Noemfoor until the end of August. On the island the Americans found emaciated forced labourers from Indonesia and auxiliaries from Formosa whom the Japanese had brought in to build airfields.

The last leap along the coast came on 30 July: units of the US 6th Infantry Division landed unopposed at Sansapor on the Vogelkop, at the western tip of New Guinea. The campaign that had begun in April with the landing at Hollandia was effectively over; in September MacArthur’s next objective became the island of Morotai, on the way to the Philippines. Against this background the 18th Army’s offensive could change nothing in the course of the war – it could only delay the dispatch of some of the troops at Aitape further west.

Place in the war

The Battle of the Driniumor proved one of the costliest of the New Guinea campaign; in the view of many historians it was surpassed in this respect only by the fighting for Buna and Gona at the turn of 1942 and 1943. Casualty figures vary depending on the source and the period covered. In the whole Aitape area, from the landing on 22 April to 25 August, the Americans counted 8,821 Japanese dead and took 98 prisoners. Japanese estimates speak of some 9,000 killed and dead out of 20,000 soldiers committed to the offensive between 1 June and 5 August – the great majority from hunger, exhaustion and disease rather than bullets. American losses in the Aitape area, including April, came to about 440 killed, 2,550 wounded and 10 missing. Four American soldiers were posthumously awarded the Medal of Honor for this fighting.

For the 18th Army the offensive was its last great offensive effort. Its remnants returned to Wewak, where they tried to survive by cultivating gardens and gathering food in the Torricelli Mountains. At the end of 1944 the Americans at Aitape were relieved by the Australian 6th Division, which fought the Aitape–Wewak campaign against the 18th Army until the end of the war. According to figures cited in the literature, of the roughly 140,000 soldiers who passed through Adachi’s army during the war, only somewhere between ten and twenty thousand survived to the surrender in September 1945. Adachi himself surrendered to the Australians on 13 September 1945 at Cape Wom near Wewak. An Australian military court sentenced him to life imprisonment for war crimes committed by his subordinates; on 10 September 1947 Adachi took his own life in a camp at Rabaul, leaving a letter in which he wrote of more than 100,000 of his soldiers who had died, mostly of malnutrition, and of having demanded of them an endurance beyond the limits of human strength.

The Driniumor showed both faces of the war in New Guinea in 1944. The Americans, though taken by surprise, had aircraft, ships, supply drops and artillery, which decided every engagement. The Japanese had courage and determination, but no food or ammunition, and their commander chose to attack because every other course seemed to him even worse. Strategically the battle changed nothing – MacArthur pressed on westwards and towards the Philippines, and the 18th Army ceased to be a force capable of offensive operations.