The Kokoda Track… [from] Gona, on the north coast of New Guinea… overland through the mountains of the Owen Stanley Range to… Port Moresby…. The Kokoda Track itself is a single-file track starting just outside Port Moresby on the Coral Sea and (depending on definition) runs 60–100 km (37–62 mi) through the Owen Stanley Ranges to Kokoda and the coastal lowlands beyond by the Solomon Sea. The track crosses some of the most rugged and isolated terrain in the world, reaches 2,250 m (7,380 ft) at Mount Bellamy, and combines hot humid days with intensely cold nights, torrential rainfall and endemic tropical diseases such as malaria. The track is passable only on foot, and as the campaign developed this had extreme repercussions for logistics, the size of forces deployed and the type of warfare that could be conducted….
The Japanese, having already captured much of the northern part of New Guinea earlier that year, landed on the north east coast of Papua on 21 July 1942, and established beachheads at Buna, Gona and Sanananda…. Japanese South Seas Force under Major General Tomitaro Horii clashed with under strength Australian forces from the Papuan Infantry Battalion and the Australian 39th Battalion on 23 July  at Awala, forcing them back to Kokoda….
At 02:00 on 29 July, the Japanese launched an attack… pouring down intense machine gun and mortar fire on the Australian position before launching an assault. Close quarters hand to hand fighting ensued…. Only after his position was completely overrun did [Watson] give the order to his troops to withdraw to Deniki. The Kokoda airstrip was captured by the Japanese who—having achieved their objective and having suffered considerable losses—did not pursue the Australians.
Although the defenders were poorly trained, outnumbered and under-resourced, the resistance was such that, according to captured documents, the Japanese believed they had defeated a force more than 1,200 strong when, in fact, they were facing only 77 Australian troops. Next to establishing the strength of the defending forces, and with the strategically vital supply base and airstrip at Kokoda within his grasp, Tsukamoto deemed the track to be practicable for a full-scale overland assault against Port Moresby. The 10,000-strong Imperial Japanese Army South Seas Force—consisting of troops from the 20th and 51st Divisions of the 18th Army, commanded by Major General Tomitaro Horii, based at Rabaul—was tasked with the capture of Port Moresby….
The Australians attempted to recapture Kokoda on 8 August without success…. [B]y 14 August they began to withdraw over the Owen Stanley Range, down the Kokoda Track towards Isurava….
By the first week in August, all the reinforcements had arrived in Deniki. The Australian force at Deniki now consisted of 33 officers and 443 other ranks of the 39th Battalion; eight Australians and 35 native troops of the PIB; and two officers and 12 native members of the Australian New Guinea Administrative Unit (ANGAU) for a total of 533 troops.[notes 4] Cameron, who believed the 'B' Company survivors' failure to hold Oivi and Kokoda against the Japanese troops indicated a lack of fighting spirit, had them sent back up the track to Eora Creek….
The Japanese advance resumed on 26 August, forcing Potts to mount a series of delaying actions as the 21st Brigade successively fell back, first to Eora Creek on 30 August, Templeton's Crossing on 2 September, and Efogi three days later on 5 September. However, the Japanese were now increasingly hampered by supply problems….
On 8 September, Rowell informed Blamey that he had decided to relieve Potts. Rowell ordered Potts to immediately report to Port Moresby "for consultations", replacing him as Maroubra Force commander with Brigadier Selwyn Porter on 10 September. The series of defeats had a depressing effect back in Australia. On 30 August, MacArthur radioed Washington that unless action was taken, New Guinea Force would be overwhelmed. General George Vasey wrote that "GHQ is like a bloody barometer in a cyclone—up and down every two minutes". MacArthur informed General George Marshall that "the Australians have proven themselves unable to match the enemy in jungle fighting. Aggressive leadership is lacking." MacArthur, concerned about the situation, wanted Blamey to go up to New Guinea and "energise" the situation by assuming personal control. Blamey had an "appallingly negative public image" with Australian troops commonly referring to him as "that bastard" and sometimes even openly booing and taunting him. Cabinet Minister Jack Beasley commented in Parliament: "Moresby is going to fall. Send Blamey up there and let him fall with it."…
On 11 September, the first reinforcements from Port Moresby arrived and took up position on Ioribaiwa Ridge to the right of composite battalion, while the 2/6th Independent Company began patrolling operations on the left. For the next two days, the Japanese heavily shelled and mortared the Australians, while infantry probed for weak spots in the position against which an assault could be launched. Before the assault could come, however, on the night of 13/14 September, the 25th Brigade—consisting of the 2/25th, 2/31st and 2/33rd Battalions—arrived to relieve the remnants of the 21st Brigade. Fresh from training in Australia and under the command of Brigadier Ken Eather, they took up positions at Ioribaiwa. Shortly afterward, however, as the Japanese launched their attack, Eather made the decision to withdraw to what he felt was a more defensible position at Imita Ridge, 40 km (25 mi) from Port Moresby. As the 25th Brigade, along with the 3rd and 2/1st Pioneer Battalions dug-in, the remnants of the 21st Brigade moved back and by 20 September the Australians had established a strong position on the ridge. The following day, they were joined by a battery of 25 pounders from the 14th Field Regiment, which had been brought up the Track, and they began patrolling operations in order to hold off the Japanese while they prepared to launch their own counter-offensive.
Upon reaching Ioribaiwa, the lead Japanese elements began to celebrate—from their vantage point on the hills around Ioribaiwa, the Japanese soldiers could see the lights of Port Moresby and the Coral Sea beyond. However, they made no concerted attempt to advance on Eather's position at Imita Ridge. Instead, Horii ordered his troops to dig in on the ridge line at Ioribaiwa….
Major General Kiyotake Kawaguchi's attack on 14 September to retake Guadalcanal was unsuccessful. In an unequal battle, Kawaguchi's forces lost about 850 killed, while the American marines lost 104. When the news reached Imperial General Headquarters in Japan, they decided in an emergency session that they could not support fronts on both New Guinea and Guadalcanal. They concluded that Guadalcanal and its airfield was essential to securing Japanese operations in the South Pacific, and Lieutenant General Harukichi Hyakutake decided that he only had sufficient troops and materiel to defeat the Allied forces on Guadalcanal.All reinforcements were being diverted to Guadalcanal and his long supply line had broken down….
Horii was now ordered on to the defensive, marking the limit of the Japanese advance southwards…