By April 1945, the Pacific War's center of gravity had moved far away. MacArthur was in the Philippines; the B-29s were burning Tokyo. On Bougainville, the Americans who had taken Cape Torokina in late 1943 had chosen a sensible plan: hold the perimeter, let the Japanese starve in the jungle behind them, and get on with winning the war. When the Australian II Corps took over in late 1944, Savige threw out the American playbook. His Militia troops - many fresh from Australia, still learning their trade - would go on the attack. The decision has been argued about ever since. Soldiers on the ground did not get a vote. They were told to march south down the Buin Road toward a river called the Hongorai, and to kill the Japanese who stood in the way.

The first fight came almost immediately. At Dawe's Creek the 24th Infantry Battalion, supported by Matilda tanks from the 2/4th Armoured Regiment, ran into concealed pillboxes and machine guns. For two days, two companies clawed across a muddy creek under more than 700 artillery shells. A bulldozer was brought forward to bridge the gap. When the position finally fell, the Australians counted seven of their own dead, nineteen wounded, and thirty-seven Japanese killed. Then they moved on toward Sindou Creek. That would be the rhythm of the whole advance - a named creek, a Japanese roadblock, a tank-and-infantry attack, a butcher's bill, another creek. In the middle of it all, Royal New Zealand Air Force Corsair squadrons roared overhead, strafing and bombing from Piva airfield to the north.

Matilda tanks were ungainly things, but in the dense Bougainville bush they were often the difference between life and death. On 5 May, along the Buin Road, the lead Matilda's machine gun jammed in front of a hidden field gun. The Japanese gunners hit it, wounding the crew. The second tank, mounting a howitzer, swung around the smoking wreck and destroyed the field gun. A company-sized Japanese counter-attack came the next morning and was beaten back after two and a half hours of fighting. One Australian died; 58 Japanese soldiers were killed. The Japanese learned quickly. They began positioning themselves off the roads where tanks could not follow, and sacrificing single artillery pieces as bait to lure Australian armour into minefields. By the time the Hongorai itself was reached on 7 May, both sides were adapting fast, under constant observation, with no place to hide.

The crossing of the Hongorai was planned for 20 May, with three battalions moving on a broad front - the 58th/59th hooking right, the 57th/60th feinting left along the Commando Road, the 24th driving straight up the middle through the Pororei ford. Between them and Buin loomed Egan's Ridge, a high feature that commanded the Australian axis of advance. The first attempt to take it, with a platoon and two tanks on 15 May, ended with a Matilda knocked out by a Japanese field gun. The RNZAF Corsairs then flew 381 sorties over eight days, while artillery and mortars fired what the official account calls, with unusual economy, "thousands of rounds." When Australian infantry finally reached the high ground, they found the ridge so thoroughly mined and booby-trapped that engineers and assault pioneers had to clear it meter by meter. The Japanese survivors had withdrawn into tunnels that a final aerial and artillery bombardment simply collapsed.

By 22 May the Hongorai was behind the Australians and the Buin Road was open. The 15th Brigade pushed on - crossed the Hari on 10 June, crossed the Mobiai in July, and handed off to the 29th Brigade for the drive on the Mivo. Then the sky broke. The Mivo rose two meters. The Buin Road, Gavin Long wrote, was reduced "to a sea of mud." Bridges the Australians had built washed out one by one. Japanese infiltrators harassed the engineers trying to rebuild them, killing men who had survived the whole advance to die on a bridge detail in the rain. When the water finally began to recede in late July, preparations resumed for the last push on Buin - the town where eight thousand Japanese still waited. Those preparations were still underway on 15 August when news of the Japanese surrender reached the island. The Battle of the Hongorai River turned out to be the last serious battle most of these Australian Militia battalions would ever fight.