Much like the Japanese base at Sanananda a large portion of the Allies at Milne Bay were devoted to non-combat tasks; building, maintaining and supplying the base and its most important component, the airfield...
Animated map of the Battle of Milne Bay
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Forces present
Of 9458 Allies present when the Japanese landed just 4500 were infantry (7th Brigade and 18th Brigade), 644 were from the Royal Australian Air Force, and 1365 were American engineers and anti-aircraft gunners. One advantage the Australians had at Milne Bay, that they did not have on the Kokoda track, was artillery. A battery of 2/5th Field Regiment was to make an important contribution to the victory
A force amounting to an Imperial Japanese Army regiment was to be available for Milne Bay but Admiral Mikawa, who ordered the operation, believed there was probably less than one battalion of Allied troops there. He decided to go ahead without waiting for Imperial Japanese Army infantry, supposing that the 2300 Imperial Japanese Navy personnel he had on hand, formed into Special Naval Landing Parties and Naval Pioneers, would be more than adequate for the task. Two light tanks, two 37mm guns and two 70mm howitzers accompanied the force.
The Japanese landing
With an escort of cruisers and destroyers the first Japanese landing, of 809 SNLP and 362 NP, took place between Waga Waga and Wandula on the northern coast of Milne Bay on the night of 25 August 1942. This was seven kilometres east of where they intended to land, a fact that had important consequences. To understand the effect of this error on the course of events it is vital to take account of the weather and the terrain. Where the Japanese landed was a narrow coastal strip between the bay and rugged mountains. There were tracks in the mountains but they ran north south, as did the ridges leading down from the mountains, while the Japanese wanted to advance from east to west, across the grain of the country. The Australians were able to block Japanese access to the airfields by the only practical approach, along the coastal flats. Secondly, almost constant rain throughout the operation turned all tracks into mud wallows and much of the area into a swamp, slowing movement. The third effect of heavy rain and banks of low cloud was on air power. The Royal Australian Air Force, with an airstrip only minutes away, could quickly sortie and attack Japanese ground troops when any break in the weather was observed. Japanese aircraft, in contrast, had to come from Buna, Lae and Rabaul. Communications with their own troops at Milne Bay often failed so they had no way of knowing when breaks in the cloud might occur there. Perhaps three quarters of all IJN air sorties over Milne Bay failed to find any targets.
On 26 August while 10th Naval Pioneers established a base the Japanese marines advanced west towards the Allied base. They encountered the Australian 61st Battalion at KB Mission. Meanwhile the RAAF struck the Japanese supply base on the beach and destroyed most of the food and ammunition.
On the night of 27 August, 61st Battalion and elements of 25th Battalion were driven back to the Gama River. There they were relieved by the 2/10th, an AIF Battalion. This battalion found it possible to advance to KB mission as the Japanese, fearing a counterattack and awaiting more marines arriving the next night, had consolidated their line near the mission.
On the night of 28 August 2/10th Battalion felt the full weight of the reinforced Japanese. Spearheading the marines, tanks split the battalion in two and drove it back. The following day the Australians prepared their next defensive position along the line of the newly constructed number three strip.
The roads remained rivers of mud. Just as the Australians were unable to get anti-tank guns to the forward troops so too the Japanese were unable to bring up their tanks which bogged short of the airstrip. The Japanese launched a major attack across the airstrip after midnight on 30 August. The assault was bloodily repulsed by 25th and 61st Battalion together with Australian artillery and American engineers. The IJN marines lost two thirds of all their casualties for Milne Bay in this disaster in which most of the senior officers were killed.
The Australian counterattack
The failure of the Japanese attack across number three strip was the turning point at Milne Bay though this was not yet clear to the commander of Milne Force, Lt General Cyril Clowes. In the morning Clowes, a Gallipoli veteran, counterattacked. The 2/12th Battalion drove forward to find the Japanese withdrawing.
Clowes always had a large superiority of numbers but until now he was rightly hesitant to do other than conserve a large reserve to ensure fulfilment of his main task - to hold the three airstrips. The presence of Japanese ships in Milne Bay most nights reminded Clowes that the Japanese might land elsewhere in the bay or at Wedau, Mullins Harbour or Taupota. He had received false reports of a Mullins Harbour landing and the Japanese did in fact intent to land at Taupota. The 353 men of the 5th Sasebo Special Naval Landing Party, en route by barge for Taupota on 25 August, were stranded on Goodenough Island when their barges were sunk by 75 and 76 Squadrons of the RAAF.
As 2/12th Battalion drove the Japanese back through KB Mission the Japanese discussed whether to reinforce or withdraw. The promised army infantry was still not available to assist and just 130 additional marines were on hand in Rabaul, so it was decided to withdraw from Milne Bay. On 4 September Clowes passed 2/9th Battalion through 2/12th but still did not throw his main weight behind the advance. He had again been advised that the Japanese ships in the bay at night indicated a new landing was being made. The Japanese ships were in fact evacuating their men and completed the task by 6 September.
The results
In all 171 Allied servicemen were killed and 216 wounded. Included in these figures were seven RAAF pilots and three Americans killed and four wounded at the defense of number three strip and in the sinking of the transport ship Anshun in the bay. In total the Japanese landed 1943 men at Milne Bay. Of these 625 died and 311 were evacuated wounded. An additional 21 Japanese aircrew were lost. While the Japanese had occasionally been temporarily repulsed in attacks in Malaya and the Philippines, this was the first time a major Japanese operation had been comprehensively defeated.