Operations during the final phase of the campaign saw the Australian forces advance north towards the Bonis Peninsula and south towards the main Japanese stronghold around Buin, although the war ended before these two enclaves were completely destroyed.

These bases allowed the Japanese to conduct operations in the southern Solomon Islands and to attack the Allied lines of communication between the United States, Australia and the Southwest Pacific Area.

According to historian Samuel Eliot Morison, this "was the one and only reason why the JCS authorized Halsey to seize a section of Bougainville: to establish forward airfields for strikes on Rabaul.

Empress Augusta Bay had a somewhat protected anchorage, and the physical barriers to the east of the cape – for instance the mountain ranges and thick jungle – meant that mounting a counterattack would be beyond the capabilities of the Japanese for weeks, if not months, which would allow the US forces to consolidate after landing and give them enough time to establish a strong perimeter.

Although MacArthur had to approve all major moves, he gave planning and operational control to Admiral William F. Halsey, Commander U.S. Third Fleet, headquartered at Nouméa on New Caledonia.

The commander of the Japanese Combined Fleet, Admiral Mineichi Koga, flying his flag aboard the battleship Musashi from Truk Lagoon, sent all of his carrier aircraft to Rabaul.

These planes would combine with the land-based air force already there and bomb Allied bases and supply routes as part of a plan the Japanese called Operation RO.

[22] Unlike on Guadalcanal and the New Georgias, Allied planners were unable to gain valuable intelligence from coastwatchers or small Australian Army detachments as the Japanese had driven them off the island long before plans for Operation Cherry Blossom began.

[17] Rear Admiral Theodore Wilkinson, Commander Third Fleet Amphibious Forces, was assigned by Halsey to direct the landings at Cape Torokina from aboard his flagship, the attack transport George Clymer.

Behind the curved sweep of the shore line, a heavy, dark green jungle...swept up over foothills and crumpled ridges to the cordillera which was crowned by a smoking volcano, Mount Baranga, 8,650 feet above sea level...It was wilder and more majestic scenery than anyone had yet witnessed in the South Pacific...[26]From the difficult landings at Guadalcanal and the New Georgias, Admiral Wilkinson had learned a significant lesson about the necessity of rapid unloading and getting his slow, vulnerable transports away from the landing area.

Wilkinson, grateful that his transports were able to land almost the entire troop contingent and a large amount of materiel unmolested by air attack, ordered them out of the area around sundown.

The two forces met in the early morning hours of 2 November in the Battle of Empress Augusta Bay, in which the Japanese lost the light cruiser Sendai and the destroyer Hatsukaze.

[29] While escorting one of the invasion echelons to the Torokina beachhead on 9 November, Morison recounts that some of Merrill's sailors witnessed an extraordinary incident that highlighted some of the extreme cultural differences at play in the Pacific: On their way north, the bluejackets topside in destroyer Spence were goggle-eyed at an exhibition of Japanese bushido.

The day after the end of the Piva Forks action, as the sixth echelon of the invasion force was unloading at the beachhead, Japanese artillery fired on the landing ships, inflicting casualties.

On 28–29 November, in an effort to block reinforcements from the Japanese 23rd Infantry Regiment, the 1st Marine Parachute Battalion carried out a raid on Koiari, about 9.3 miles (15 km) east of Torokina.

The Japanese Army command at Rabaul was certain that the Allies would be moving on from Torokina; Imamura ordered a build-up of the defenses at Buin, on the southern tip of Bougainville.

[46] In November and December the Japanese emplaced field artillery on the high ground around the beachhead, concentrated in a group of hills along the Torokina River overlooking the eastern perimeter.

[52] Rabaul had already been raided multiple times between 12 October and 2 November by the heavy bombers of General George C. Kenney's Allied Air Forces Southwest Pacific Area.

Morison attributes this to previous losses inflicted against the Japanese air arm, writing that the fact such a large fleet "could set thousands of troops ashore with impunity only 115 miles from Rabaul proved what good work AirSols had already accomplished.

[59] In describing the effect, Morison writes: "it is significant that the splendid harbor which in October 1943 had held some 300,000 tons of enemy shipping, and had sheltered powerful task forces of the Japanese Navy, was reduced to a third-rate barge depot.

[69] On 5 April the Americal Division's 132nd Infantry Regiment, after establishing patrol sweeps along Empress Augusta Bay, successfully launched an attack to capture the Japanese-held village of Mavavia.

[69] According to Morison, amongst the Japanese troops "morale fell deplorably ... after the loss of the Battle of the Perimeter; Admiral Takeda, in his narrative, notes robberies, insubordination and even mutiny.

"[74] Australian intelligence officers, after studying records, estimated that 8,200 Japanese troops had been killed in combat during the American phase of operations, while a further 16,600 had died of disease or malnutrition.

[83] Pursuant to Savige's 31 December order to begin operations in the northwestern sector at the first opportunity, General J.R. Stevensons's 11th Brigade advanced along the coast, reaching the village of Rukussia by mid-January 1945.

Because the 11th Brigade was exhausted from three weeks of jungle combat, frontal assaults were ruled out and an attempt was made to outflank the Japanese positions with an amphibious landing on 8 June.

Although Japanese losses in the resulting Battle of Porton Plantation were probably higher, the defenders received a boost in morale, and the Australian command called off offensive operations in this sector for the time being.

Having learned a costly lesson about the ineffectiveness of banzai charges, Kanda pulled his men back to a defensive perimeter around Buin and reinforced them with the garrisons from the Shortlands and the Fauros.

However, shortly after reaching the Mivo River their advance came to a halt as torrential rain and flooding washed away many of the bridges and roads upon which the Australian line of communications depended.

This rendered large scale infantry operations impossible for almost a month, and it was not until late July and into early August that the Australians were able to resume patrolling across the Mivo River.

[91] Before Savige could mount a substantial assault, news arrived of the dropping of the atomic bombs, after which the Australian forces mainly only conducted limited patrolling actions.