The Japanese plan had been born out of failure. In May 1942, a seaborne attempt on Port Moresby had turned back in the Coral Sea, and the invasion force had retreated to Rabaul. The 17th Army, under Lieutenant General Harukichi Hyakutake, had to find another way. Pre-war intelligence suggested a road ran from the village of Kokoda south to Port Moresby, across the central spine of Papua. Aerial reconnaissance by the 25th Air Flotilla on 27 and 30 June seemed to confirm a track from Buna inland. Planning moved quickly. Major General Tomitarō Horii's South Seas Detachment, the same troops who had prepared for the canceled sea landing, would go overland instead. The trouble was that the aerial photographs showed a footpath, not a road. The central cordillera is one of the most brutal pieces of terrain on Earth. Nothing the Japanese had trained for - no fleet of trucks, no wheeled artillery, no column of supply wagons - could cross it.

The Australians had perhaps a hundred men forward of Buna when the landings began, most of them members of the Papuan Infantry Battalion, a unit of Papuan soldiers under Australian officers. Templeton, their commander at Kokoda, had actually been at Buna the morning of the landing and was returning inland when word reached him. He ordered 11 Platoon to meet him at Awala and 12 Platoon to push forward to Gorari. On the afternoon of 23 July, a PIB patrol led by Lieutenant Chalk engaged the advancing Japanese near Awala. The exchange was brief and one-sided. The Japanese returned heavy fire, and most of the patrol, in the words of the Australian war diary, "fled into the jungle." This is not a criticism. It is a description of what small Papuan and Australian units, outnumbered more than thirty to one, could actually do in first contact with a professional army. They could slow the advance. They could blow a bridge. They could report what they saw. That was all.

What followed was a fighting retreat across the foothills of the Owen Stanley Range. On 24 July, Major William Watson of the PIB destroyed the bridge over the Kumusi River at Wairopi, then harassed the Japanese as they crossed. Lieutenant Colonel William Owen flew in to Kokoda with reinforcements. On 25 July, an Australian ambush east of Gorari killed two Japanese soldiers and withdrew to Oivi. The following day, the 39th Battalion's 16 Platoon arrived at Kokoda by air in two flights; the first was rushed forward and joined the fight at Oivi before the 15:00 Japanese attack. When the second half of the platoon was delayed, Templeton walked out to warn them. A burst of gunfire echoed up the track. He never returned. Japanese records, uncovered by historian Peter Williams decades later, show that Templeton was captured and subsequently executed. His body was never recovered by Australian forces.

Among the Europeans in the Buna area when the Japanese landed were two young missionaries, May Hayman and Mavis Parkinson. They fled into the bush with a small mixed party - members of the PIB, Australian Army signallers, several American airmen whose aircraft had gone down. For weeks they moved through the jungle, trying to reach Allied lines. In August, the party was ambushed. The survivors were captured, interrogated, and executed by members of the 5th Sasebo Special Naval Landing Force. Nine Europeans were killed at Buna, including a sixteen-year-old girl. These were not combatants. They were two mission workers, support personnel, and downed airmen who had tried to hide in a country that had nowhere left to hide them. The Australia-Japan Research Project would later document the killings as war crimes - a pattern that would repeat across the Pacific in the months that followed.

By late August, Horii had roughly 13,500 men ashore between Buna and Gona. The 144th Infantry Regiment's main force landed on 18 August. The 41st Infantry Regiment came in on 21 and 27 August. Yokoyama had already taken Kokoda in a fight on 28-29 July and pushed the Australians back again at Deniki on 13-14 August. The overland advance to Port Moresby would begin within days. The historian David Horner, who has spent his career studying this campaign, identifies several points where Douglas MacArthur could have stopped what was coming. Intelligence had warned of the Japanese intent to occupy Buna before the landings. MacArthur did not move to hold the beachhead first. When the Japanese came ashore, the overland route south was not recognized for what it was, despite further intelligence. Horner writes that MacArthur had actually intended to let the Japanese attempt the march - and then his actions during the campaign that followed, Horner notes, became inconsistent in ways that would cost Australian, American, and Papuan lives for months to come.