The final battle involving Australian troops in 1942 was the Allied attack on the Japanese beachheads in northern Papua – Buna, Gona and Sanananda. The Allies expected that this battle would be won easily, as it seemed that the Japanese had lost most of their force in Papua in the long battle on the Kokoda Track. In the last pitched battle on the Kokoda Track, at Oivi-Gorari, the Australian 16th and 25th Brigades had overrun the dug-in survivors of the Japanese 144th Regiment and the way seemed clear to the coast.
In fact, the senior Allied commanders – Generals Douglas MacArthur, the American supreme commander of Allied forces in the South-West Pacific Area, and Thomas Blamey, the Australian commander of Allied Land Forces in the theatre – grossly underestimated the strength of the Japanese force and overestimated the Allies' capacity to continue fighting.
The Japanese had brought in fresh troops and had up to 9000 men in well-dug defences around the beachheads who were prepared to fight to the death if necessary. Of the troops first detailed to attack, the 16th and 25th Brigades were down to one-third of their normal strength and were worn out after fighting their way across the mountains, while fresh American troops from the 32nd Division were not adequately trained for jungle warfare and had no combat experience.
The battle opened on 19-20 November with simultaneous attacks against Buna by the Americans, Gona by the Australians and Sanananda by both Australians and Americans. The troops encountered a string of well-defended bunkers, expertly camouflaged in the lush tropical vegetation, and enemy troops armed with machine-guns and mortars. American troops suffered heavy casualties, and so did the Australians. The Allied attacks faltered on all fronts.
Bogged down, the Allies built airfields not far from the battlefronts so that supplies and reinforcements could be flown in from Port Moresby. The air war over the beachheads was vital. American fighters patrolled the area to chase away any Japanese aircraft so that Allied aircraft could continue to transport and supply troops. On many days, cloud over the Owen Stanley Range either prevented flying or limited the number of flights that could be flown, and on these days troops in the forward area ran low on food and ammunition.
Allied aircraft and artillery bombed and shelled the Japanese positions, but the Australian and American troops continued to suffer heavy casualties in attacking them. Not only did enemy fire cause the death and wounding of many men, but tropical diseases such as malaria caused many more to be evacuated sick. Allied commanders pondered whether it was the Japanese or the mosquitoes that represented the worst enemy. They reasoned that at least the Japanese were also suffering with the same tropical diseases as their own men.
By the end of November, the Australian 21st and 30th Brigades, including many veterans of the Kokoda Track, had been flown in to relieve the exhausted 16th and 25th Brigades. On 9 December, the 21st Brigade captured Gona after suffering heavy casualties in repeated attacks. Meanwhile, the Americans at Buna had also made some ground but, having taken heavy casualties, had to be reinforced by the Australian 18th Brigade, which had earlier fought at Milne Bay. Over the rest of the month, with support from Australian light tanks, this brigade made steady progress in pushing back the enemy at Buna, but suffered hundreds of battle casualties.
The battle for the beachheads dragged on into the middle of January 1943, by which time only the enemy pocket around Sanananda remained. The 30th Brigade, which was comprised of inexperienced militiamen reinforced by other inexperienced troops, had suffered over 50 per cent casualties attacking along the Sanananda Track and made little further progress. The 18th Brigade was moved over to the Sanananda front to take over from the 30th, after finishing off the last Japanese resistance at Buna. Swamps in this area prevented the use of tanks and the battle again bogged down.