This was the New Zealand and US seizure of the Treasury islands group within the Solomons islands group (27 October/3 November 1943).
The Treasury islands group is located just to the south of the southern tip of Bougainville and 15 miles (24 km) to the south-west of the Shortland islands group. The largest island is Mono island to the north, while Stirling island to the south encloses the anchorage of Blanche Bay. Mono island is dominated by three volcanoes reaching a maximum height of 1,053 ft (321 m). The only suitable landing beaches were near the village of Falamai on Mono island’s south coast near the eastern entrance to Blanche Bay. Almost completely undeveloped when war broke out, Mono island had a primitive road net supporting a number of copra plantations, and had been occupied by the Japanese early in 1942.
The islands had been scouted by US Marine raiders from the submarine Greenling on 22/23 August 1943, and again by PT-boats on 21/22 October. The scouts reported that the Japanese garrison numbered just 225 men.
The 'Goodtime' operation was planned as a support for the impending 'Cherryblossom' landing on Bougainville island, and was undertaken by Brigadier R. A. Row’s 8th Brigade Group (29th, 34th and 36th Battalions as well as supporting elements including one field artillery regiment and one light anti-aircraft artillery regiment) of Major General H. E. Barrowclough’s 3rd Division assigned to the I Amphibious Corps. Row commanded a combined force augmented by US Army anti-aircraft units, US Navy 'Seabee' construction battalions and base elements, and small US Marine communications and air liaison detachments, the force totalling 4,608 New Zealand and 1,966 US troops, including 3,795 men for the initial landing.
To aid 'Cherryblossom', the operation was to take Mono island for the establishment of a radar station, and Stirling island for the establishment of a staging area for 'Cherryblossom'.
The Allied force was supported by six destroyers and 32 aircraft, while the Japanese had more than 240 men and 49 aircraft. The invasion force made a practice landing on Florida island, and departed Guadalcanal and the Russell islands group on 23/26 October 1943.
The Allied undertaking was supervised by Rear Admiral George H. Fort, the US officer commanding the 5th Amphibian Group, and the main landings comprised three waves delivered by eight transport destroyer conversions, eight infantry landing craft, two tank landing ships, eight mechanised landing craft, three tank landing craft and two coastal transports escorted by destroyers Conway, Cony, Eaton, Pringle, Philip and Renshaw. A novel feature of this landing was the use of two gun-armed infantry landing craft, the first such craft so modified in the Pacific. Eaton provided fighter direction while Pringle and Philip undertook a gunfire bombardment of the landing areas.
The South Force (Task Unit 31.1) of Task Force 31 (3rd Amphibious Force) arrived at the eastern entrance of Blanche Harbour, between the larger Mono island and smaller Stirling island, at dawn on 27 October. A Japanese aeroplane spotted the force as it approached the islands, but the Japanese were nonetheless taken by complete tactical surprise. Divided into the Northern and Southern Landing Forces for Mono and Stirling respectively, the landing craft entered Blanche Harbour with unco-ordinated fire support provided by destroyers, landing craft, infantry landing craft (gun) in their first operational mission, and aircraft. The destroyers had to remain outside the harbour because of the lack of manoeuvring room.
Resistance was light, although one tank landing ship came under heavy machine gun fire from a hidden pillbox when it lowered its bow ramp. The New Zealanders aboard commandeered a 'Seabee' bulldozer and used its blade as an armoured shield to advanced and bury the pillbox under coral sand.
Automatic weapons fire was received from the village of Falamai on Moro and also from Stirling. Two battalions of New Zealanders landed to the east of the mouth of the Saveke river less and 880 yards (805 m) to the west of Falamai at 06.06. The Japanese were emplaced at the river mouth and in the village. Another battalion landed on Stirling’s north central coast without opposition at the same time. On Mono the beach-head soon came under artillery and mortar fire as the two battalions cleared the high ground around Falamai and established a perimeter round Blanche Bay for the night.
There was a subsidiary landings on Stirling island, which was found to be unoccupied.
Though caught off their guard, the Japanese responded with their customary swiftness and air attacks began in the afternoon. An initial attack was made by 25 Aichi D3A 'Val' dive-bombers, but these lost 12 of their number to the Allied anti-aircraft fire and fighter cover, and in return inflicted only minor damage on Cony with two bomb hits. But much of the Japanese garrison was destroyed in the first day and Allied casualties were very light.
A third landing took place at the village of Soanotalu on Mono’s north central coast at the same time as the main landings, the unit in this case being 'Logan' Force, a New Zealand infantry company escorting a US Navy air-warning radar unit. Landed without opposition, the radar was soon operational to provide warning of air raids from air bases on Bougainville and New Britain islands. There were also two Japanese counterattacks against the Soanotalu beach-head, starting on 1 November with an 80-man assault and ending on the following day, by troops desperate to capture the Allied landing craft and escape the island. By this time, the 'Seabees' had constructed a pillbox, two platoons had been relocated from Stirling Island to Soanotalu. The New Zealanders beat back these counterattacks and then hunted down the survivors.
Most of the surviving Japanese fled into the hills and headed for the north coast in the hope that they would be evacuated by sea. The Japanese had 25,000 troops and a large number of landing craft and barges on Shortland island and at Buin on the southern end of Bougainville island, a mere 22 miles (35 km) to the north-east of Mono island, but these did not intervene.
On 28 October a New Zealand company moved cross-country to secure the village of Malsi on the east coast, and took this on 31 October. On 1 November, after the arrival of support elements, the New Zealanders started a series of sweeps of Mono island’s rugged interior to hunt down the stragglers. The island sweep was completed on 5/6 November, and on 12 November Moro was declared secure after 305 Japanese had been killed and eight taken prisoner. The Allied losses ashore were 40 New Zealanders killed and 145 wounded, and 12 US troops killed and 29 wounded.
In conjunction with the 'Blissful' operation on Choiseul island, 'Goodtime' served to distract the attention of Lieutenant General Haruyoshi Hyakutake’s 17th Army from the island of Bougainville, which was in fact the next major target for the forces of Admiral William F. Halsey’s South Pacific Area command as it contained six important airfields which had been bombed enough to destroy Japanese aircraft but not to ruin the facilities. The Japanese air raids ended after the 'Cherryblossom' landing on Bougainville island on 1 November.
Work had started immediately after the 'Goodtime' landing and the establishment of a beach-head perimeter on the creation of supply dumps, a PT-boat base and a fighter airfield on Stirling island. The 5,600-ft (1705-m) runway was ready late in November and this was extended to 7,000 ft (2135 m) during December so that bombers could use it. Docking facilities were built and the Naval Advance Base, Treasury Islands, supported the campaigns in the northern part of the Solomon islands 'chain' and in the Bismarck islands group into 1944.
By a time late in 1944 much of the base had been dismantled, and it was disestablished in March 1945, though maintenance elements remained until June.