Colonel Yokoyama Yosuke, commander of 15 Independent Engineer Regiment, led the 'Yokoyama advanced force' ashore unopposed at Basabua in the late afternoon of 21 July 1942. Before dawn the following morning all troops, equipment and supplies disembarked and the ships had sailed, so as to be clear of the coast when Allied aircraft arrived looking for them. A week later a second convoy brought the rest of Yokoyama's force giving him 4020 men including 1200 carriers from New Britain.

By then the foremost Japanese troops were almost at Kokoda. The night of the first landing, as soon as trucks could be unloaded, a company of infantry was driven inland. When the road ended the Japanese loaded their equipment on to carts and bicycles and continued their rapid advance. On 23 July the first engagement of the campaign took place near Awala when 38 men of the Papuan Infantry Battalion, under Major William Watson, fired on the Japanese then retired. A private of the Papuan Infantry Battalion said that they each fired eight or nine rounds, 'then Major Watson told us to run for our lives'

Later that day a platoon of 39th Australian Militia Battalion also briefly delayed the Japanese. Similar short clashes took place on 24 July at the crossing of the Kumusi River and on 25 July at Gorari. Thus far all the encounters had been of only a few minutes duration and were fought between 40 or so Papuans and Australians and the Japanese advanced guard, but the next engagement at Oivi was a more serious affair.

When the Japanese landed the widely dispersed defenders in the region numbered 420 men of the PIB, the Royal Papuan Constabulary and B Company of 39 Battalion. By 26 July 145 men, of all three units, had been collected at Oivi, 16 kilometres east of Kokoda. Watson and Captain Samuel Templeton, of 39 Battalion, decided to make a stand. The Japanese were held up for several hours until, threatened with encirclement, the Papuans and Australians retreated. During the Oivi engagement Templeton, after whom Templeton's Crossing on the Kokoda track is named, was wounded and captured. He was later interrogated then executed.