The battle of Milne Bay (25 August-7 September 1942) was the first defeat suffered by Japanese land forces during the war in the Pacific, and prevented them from establishing a base at the eastern tip of New Guinea.
The Japanese had attempted to establish a foothold on the south-eastern shore of New Guinea in May 1942, but had been turned back at the battle of the Coral Sea. They had then landed a strong force at Buna, at the northern end of the Kokoda Trail, a mountain track that crossed the Owen Stanley Range and ended at Port Moresby. By August the Japanese were making slow progress along this track, and decided to occupy Milne Bay in order to construct an airfield from where they could threaten Port Moresby.
Allied interest in Milne Bay began on 8 June, when a small party of Australians and Americans flew out to the area to search for a suitable sight for an air base. Their mission was a success, for on 12 June GHQ, South West Pacific Area, authorized the construction of air bases around the head of Milne Bay.
A small Allied garrison – two companies and a machine gun platoon from the Australian 15th Brigade – sailed for Milne Bay from Port Moresby on 22 June, arriving three days later. They were followed on 29 June by Company E of the US 46th Engineers, who began work on the new airfields, which were soon operational. By the time the Japanese attacked Nos.75 and 76 Squadrons of the Royal Australian Air Force, equipped with P-40 Kittyhawks, and No.6 Squadron (RAAF), with the Lockheed Hudson, were all flying from the new airfields.
The garrison was dramatically increased in size before the Japanese arrived. During July the Australian 7th Militia Brigade was ordered to Milne Bay, and on 21 August it was joined by the 18th Brigade, an experienced regular force under the command of Brigadier George Wooten. Including the American engineers, and the US 709th Airborne Anti-Aircraft Battery, the defenders of Milne Bay numbered around 8,700, under the command of Major-General Cyril Clowes (as well as 664 men from the RAAF).
Tokyo ordered an all-out offensive in eastern New Guinea on 28 July. By 20 August the details of the attack on Milne Bay had been worked out. 1,500 troops were to be transported from Kavieng, New Ireland and Buna, with orders to land at Rabi, from where they were to launch an immediate attack towards No.3 Airstrip, the eastern-most of three airfields being built at Milne Bay.
The Japanese force departed for Milne Bay on 24 August. The troops from New Ireland travelled in large transports, but the troops from Buna set out in seven large landing barges. That afternoon the barges were spotted one of the coastwatchers. On 25 August a force of P-40s from the airfield at Milne Bay found the barges while they were beached on Goodenough and D’Entrecasteaux Islands, off the north-eastern corner of New Guinea, and destroyed all seven of them.
Air attacks on the transports from New Ireland were less successful, and after shelling the beaches the Japanese were able to land three miles to the east of Rabi. During the night of 25-26 August the Japanese ran into part of the Australian 61st Militia Battalion, posted at K. B. Mission, half way between their landing zone and Rabi.
The battle for Milne Bay took place along a road that followed a narrow strip of level ground on the northern shores of Milne Bay, running east from No. 3 Airstrip to Kilabo, Rabi, Motieau, K. B. Mission, Goroni and Waga Waga.
On the night of 25-26 August the Australian Militia held their ground, and at dawn on 26 August the Japanese withdrew to their landing position. During the day Allied aircraft from Milne Bay and Port Moresby attacked the Japanese position, destroying most of their supplies and sinking one transport ship, but after dark the Japanese were able to land the rest of the force from New Ireland, bringing the invasion force up to 1,170 men.
On the night of 26-27 August this larger force was able to push the Australians back to the Gama River, between Rabi and Motieau, but once again at dawn they pulled back to their landing positions. During daylight on 27 August part of the Australian 18th Brigade advanced as far as the K.B. Mission, but on the night of 27-28 August the Japanese made a strong attack, reinforced by light tanks, and forced the Australians back almost to the edge of No. 3 airstrip.
The crisis of the battle came on 28-30 August. On 28 August the Japanese made a determined frontal assault on the airstrip, but were successfully held off. On the following day 775 Japanese reinforcements reached Milne Bay, and on the night of 30-31 August the Japanese launched their final attack on the airstrip. This final attack ended in a costly defeat, and on 31 August the Australians were able to go onto the offensive.
By the end of 31 August 18th Brigade had reached K. B. Mission for the second time, this time to stay. Over the next few days the outnumbered Japanese were forced steadily back, and on 4 September the Australians reached Goroni, east of the original Japanese landing point and close to their supply dump at Waga Waga. On the night of 4-5 September the Japanese began to load their wounded onto ships, ready for a retreat. The evacuation was completed on the night of 5-6 September. About 1,300 Japanese troops were evacuated by sea, under cover of a regular naval bombardment. Of the remaining 600 troops sent to Milne Bay, most had become casualties, although a small number remained behind, and continued to fight until 7 September.
The successful defeat of Milne Bay was the first permanent defeat inflicted on the Japanese in landing fighting since the start of their series of lightning conquests in December 1941. It proved that the Japanese soldiers were not invincible in the jungle, although they had been outnumbered by four-to-one and subjected to constant air attack during the battle. More significant was the defeat the Japanese were about to suffer on the Kokoda Trail, where on 25 September the Australians launched the counterattack that would push the Japanese back across the Owen Stanley mountains.