Battle of the Green Islands

The Battle of the Green Islands or Operation Squarepeg was fought from 15 to 20 February 1944, between Imperial Japan and Allied forces from the New Zealand 3rd Division and the United States. Undertaken after landings to secure lodgments on New Britain and Bougainville, the main focus of the operation was the capture of Nissan Island, which was secured by New Zealand forces after only a short ground campaign. At only very limited cost in terms of casualties, the Allied operation resulted in the capture of several small atolls in the island chain, which were subsequently used to support air and naval operations focused on reducing the main Japanese base on Rabaul.

The Green Islands, consisting of several small coral atolls, are located between Bougainville and New Ireland, about 150 mile (241 km) from Rabaul, which was the location of the main Japanese base in the area. At the time of the battle, they were part of the Australian Territory of New Guinea and were populated by around 1,200 Melanesians. The atolls form a rough circle, with the main island, Nissan, forming a west facing crescent shape closed off by several smaller islands separated from the main landmass by small passages that open up into a large internal lagoon roughly in width. In the wake of landings at Cape Gloucester and Cape Torokina on New Britain and Bougainville, the Allies sought to continue their offensive operations in the region, as part of the advance towards the Japanese base around Rabaul, prior to launching the Admiralty Islands campaign. The Green Islands were subsequently identified as being close enough to fighter cover provided by aircraft based at Torokina, while offering the prospect of projecting Allied air and naval power further towards Rabaul. On 30 January 300 troops from the New Zealand 30th Infantry Battalion, along with American and New Zealand intelligence and communications personnel, were landed on Nissan Island. Escorted by a small naval force including several destroyer escorts, motor torpedo boats and landing craft, the party was tasked with determining the strength of the Japanese there as well as siting landing beaches and determining prospects for base development.

Under the command of Admiral William Halsey Jr., the invasion of the islands commenced on 15 February 1944, codenamed "Operation Squarepeg". Staging out of Vella Lavella and the Treasury Islands, Allied forces invaded several islands, including Nissan Island, and recaptured them from heavily outnumbered Japanese forces (estimated at around 120 to 150 strong). The Japanese garrison consisted of 12 naval watchkeepers and about 80 army personnel from Hitoshi Imamura's Eighth Area Army, that had been landed by submarine in early February. This small force was reinforced further, reaching around 120. The infantry were transported aboard US Navy high speed transport (APDs). These were escorted by a strong naval task force of destroyers, minesweepers and motor torpedo boats, under the command of Rear Admiral Theodore Wilkinson, while American LSTs landed the 3rd NZ Division Special Army Tank Squadron's Valentine tanks. Logistical support was provided by several Seabee battalions (the 33rd, 37th and 93rd), as well as various other naval base and survey units. A US coastal artillery battalion was also landed to provide anti aircraft defence, as were armoured, engineer, artillery, medical and other divisional logistic support units from the New Zealand 3rd Division. The fighting was brief but sharp on land with heavier resistance in the air. Prior to the landing, as the assault force steamed towards the islands, a large group of Japanese aircraft were dispatched from Rabaul to attack the naval task force. The landing craft and transports escaped damage, but the cruiser St. Louis, which formed part of the southern covering force, was hit resulting in 23 killed and 28 wounded. Later, a group of dive bombers appeared over the landing craft as they were forming up to the west of the islands, but the Japanese aircraft were promptly dealt with by the escorting AirSols fighters from Cape Torokina, which quickly gained control of the air over Nissan Island. In all, the Japanese lost 12 aircraft. Apart from a near miss on LST 446, the landing proceeded quickly and smoothly. After being crossloaded from the transports, the infantry were ferried ashore in LCIs and LCP(R)s, which proceeded to enter the lagoon to the south of Barahun Island. Troops disembarked at several landing beaches around the Pokonian and Tangalan Plantations. In total 5,800 personnel were landed on 15 February, of which over 4,200 were New Zealanders. The perimeter was held throughout the night. Each infantry battalion was supported by a troop of Valentine tanks, which provided close support and helped clear tracks through the jungle. A series of minor patrol actions took place in the 30th Battalion's area of responsibility, while a group of around 70 Japanese was encountered around a Catholic mission around the southern end of the island near Tanaheran, having become caught between patrols from both the 30th and 35th Battalions. This group of Japanese were overwhelmed over the course of several days by New Zealand infantry, supported by several tanks, at the cost of three killed and 11 wounded, while 62 Japanese were killed. On 23 February, the final action of the campaign took place when a company sized patrol from the 37th Battalion cleared the small island of Sau, where 14 Japanese survivors had withdrawn. After refusing a call to surrender, the small Japanese force was destroyed in a brief firefight that resulted in four New Zealanders being wounded. Overall casualties for the entire operation amounted 13 killed and 26 wounded for the Allies, while almost all of the Japanese garrison was killed. The airstrips became home to United States Marine Corps fighters and bombers which participated in the Allied effort to isolate the Japanese bases on Rabaul and Kavieng, while New Zealand fighters also used the base to refuel during operations over Rabaul. A South Pacific Combat Air Transport Command (SCAT) detachment, which supplied materiel and mail to combat soldiers and evacuated the wounded, was also established on the island. Lieutenant Richard Nixon, who later became President of the United States, served as the officer in charge of the SCAT detachment on the Green Islands in early 1944. Other base facilities included a coral seaplane ramp, and three moorings with concrete anchors and oil drum buoys. A fuel pier was constructed, and an entire PT boat base with camps, workshops, a steel warehouse, and a T shaped pontoon pier. Medical facilities were provided for a naval base hospital with four Quonset huts. Base construction was considered complete by July 1944, and responsibility for the installations was handed over to Construction Battalion Maintenance Units (CBMU) 552 and 553. They began dismantling the base in late 1944. CBMU 552 left in March 1945, but CBMU 553 remained until August 1945.