'Squarepeg' was New Zealand seizure of Nissan island, the largest of the Green islands group between the north-western tip of the Solomon islands group and the south-eastern tip of New Ireland, by Brigadier L. Potter’s 14^th Brigade Group of Major General H. E. Barrowclough’s 3^rd Division (15/20 February 1944).

The Green islands group comprises a number of small atolls n the area to the north of Bougainville island and to the east of New Ireland island. The largest of these islands is Nissan, which is 9 miles (14.5 km) long and 5 miles (8 km) wide, and encloses a central lagoon which is accessed by two passes in its north-western quadrant. Nissan is fringed by reefs to the north and south, but there are beaches suitable for amphibious landings on its eastern shore. The island is heavily vegetated and, though generally flat, has areas of raised ground to the east and south. The population in 1941 was about 1,150 Melanesians engaged in the production of copra and taro.

The Japanese had occupied Nissan at a time early in 1942. The only Allied presence on the island was a coast watcher, C. C. Jarvis, who radioed the presence of an unknown ship at the lagoon entrance but then disappeared. On Nissan island the Japanese presence then came to comprise only a barge staging base to support the movement of men, equipment and supplies between their base areas on New Britain and New Ireland and the forces in the Solomon islands group, most especially Buka off the north-western tip of Bougainville island, and the larger Bougainville island itself. Even after the Allies had established themselves on Bougainville in 'Cherryblossom', the Japanese did not see fit to establish any real force on Nissan island as an outpost of Rabaul and Kavieng, a task for which the island would have seemed to be admirably suited: Rabaul lies only 115 miles (185 km) to the west and Kavieng 220 miles (355 km) to the north-west.

Conversely, the Allies wished to secure a foothold in the area to the east of Rabaul from which to interdict traffic on the barge route linking Rabaul and Bougainville island via Buka, and to attack Kavieng and other bases on New Ireland. The Tanga islands group, only 25 miles (40 km) east of New Ireland and about 70 miles (115 km) to the north of the Green islands group, was initially considered but then rejected as being too far distant for fighters from Bougainville island to remain on station for a tactically useful period. The establishment of beach-heads at either or both of the two Japanese airfields on New Ireland’s east coast would require large landing forces and carrierborne air support. However, the Green islands group lay within land-based fighter range of Bougainville and was only weakly defended.

Following the success of the 'Cherryblossom' and 'Backhander' landings on Bougainville and Cape Gloucester respectively, the majority of the naval forces under Admiral William F. Halsey were withdrawn to participate in the Central Pacific offensive. As a result, Halsey would not have sufficient naval strength to support a landing at Kavieng until April 1944. Concerned by the possible consequences of taking the pressure off the Japanese for three months, Halsey decided to take the easier objective of Nissan, which would maintain the Allied pressure on Rabaul and also bring Allied air power within range of the major Japanese base at Truk atoll in the Caroline islands group.

Late in December 1943, therefore, the Allies decided to seize both the Green islands group and the Admiralty islands group, the latter lying to the north-west of New Britain and New Ireland, during February 1944.

Little was known of Nissan, so the Allies planned two adventurous reconnaissance missions. On 10/11 January 1944 four PT-boats from the base at Torokina on Bougainville island examined the lagoon channels, finding the South Channel deep enough to allow the passage of tank landing ships. The next step was a reconnaissance in force executed on the night of 30/31 January, so close in time to the launch of 'Squarepeg' that the Japanese would not have time to reinforce the garrison. The fast transports Stringham, Talbot and Waters, escorted by the US destroyers Fullam and Guest, landed 322 men of Lieutenant Colonel F. C. Cornwall’s New Zealand 30^th Battalion and a 27-man US survey team to Nissan island at 24.00. The transports withdrew and the force scouted the island, selecting landing beaches and an airfield site, verified the depth of the lagoon and its freedom of dangerous coral heads, and interviewed members of the native population who were, in general, hostile to the Japanese. The 72 men of the Japanese garrison, who had pulled back to the southern end of the atoll, fired on one of the landing craft and killed four men. They were of no further trouble and the reconnaissance force did not pursue them. An air attack was launched from Rabaul, but inflicted no damage. This preliminary operation’s naval commander felt that the island could have been secured at the time, but as there were the threat of more air attacks from Rabaul and no Allied plan for immediate reinforcement, the reconnaissance force withdrew on the following day as planned.

As in 'Goodtime' by Brigadier R. A. Row’s 8^th Brigade Group of the same division against the Japanese on Treasury island, between Vella Lavella and New Georgia in October 1943, the armour-reinforced 14^th Brigade Group, strengthened with US anti-aircraft units, a number of base units, and three 'Seabee' and two 'Acorn' construction units, was earmarked for 'Squarepeg' under the tactical leadership of the divisional commander with Rear Admiral Theodore S. Wilkinson’s 3^rd Amphibious Force supervising the operation.

The landing force was carried in nine troop-carrying destroyer conversions, and these were escorted by the destroyers Bennett, Fullam, Guest, Halford and Hudson, 12 infantry landing craft escorted by the destroyers Philip, Pringle, Saufley, Renshaw, Sigourney and Waller, and seven tank landing ships escorted by the destroyers Anthony, Braine, Conway, Eaton, Terry and Wadsworth. Cover to the north and east was the task of Rear Admiral Aaron S. Merrill’s Task Force 39 with the light cruisers Columbia and Montpelier, and five destroyers, and to the south was the responsibility of of Rear Admiral Walden L. Ainsworth’s TF38 with the light cruisers Honolulu and St Louis (damaged on 14 February by a Japanese dive-bomber) and five destroyers.

During the night 17/18 February Destroyer Squadron 12 fired 3,868 5-in (127-mm) shells into Kavieng from destroyers Farenholt, Buchanan, Lansdowne, Lardner and Woodworth, and Destroyer Squadron 23 lobbed 6,681 5-in (127-mm) shells into Rabaul from Charles Ausburne, Dyson, Stanly, Converse and Spence. During the night of 22/23 February Destroyer Squadron 12 shelled Kavieng once again, on 24/25 February Destroyer Squadron 45 shelled Rabaul with Anthony, Bennett, Braine, Fullam, Guest, Halford and Hudson, and on 29 February/1 March Destroyer Squadron 22 repeated the process with Waller, Conway, Eaton, Philip, Pringle, Renshaw, Saufley and Sigourney.

The Green Islands Attack Group departed Vella Lavella and the Treasury islands group on 12/13 February. The group was sighted by Japanese air reconnaissance during the night of 14/15 February, and an attack by 32 aircraft from Rabaul damaged one of the cruisers in Ainsworth’s covering force. A second attack by 15 unescorted Aichi D3A 'Val' dive-bombers arrived over the group at 06.41, shortly after the landing craft had been manned, but the Japanese warplanes were intercepted by 32 US land-based fighters and effectively destroyed.

The Green Islands Attack Group arrived off Nissan atoll’s western side and sent landing craft though South Channel after first light. Two battalions landed without opposition on two beaches on the lagoon’s eastern side at 07.00, and then turned north and south to cover the island’s length. Another battalion landed at 06.55 on another beach at the end of the lower arm of the atoll and secured the lagoon’s entrance. By the fall of night on 15 February some 5,800 men had been landed.

Even though Allied aircraft had been attacking Rabaul and Kavieng for two weeks, the Japanese were nonetheless able to launch significant air attacks, which in fact accomplished little. The only air attacks which followed this initial air effort were nocturnal bombing raids intended largely as harassment efforts.

The original Japanese garrison of General Hitoshi Imamura’s 8^th Area Army had fled to the Feni islands group, some 35 miles (55 km) to the north, on 1 February after the initial New Zealand reconnaissance in force. About one-third of the garrison had returned on 5 February and then been reinforced by a 77-man naval guard detachment delivered from Rabaul by submarine. There were 102 Japanese on the island at the time of 'Squarepeg', about 40 of them dug in around the Catholic mission on Nissan atoll’s southern end. Here there were destroyed between 16 and 19 February after a final counterattack. The Japanese also lost 12 aircraft at the cost to New Zealand of 13 men killed and 26 men wounded.

The island was declared secure on the following day. A PT-boat base was immediately established, and the construction units had completed an airfield by the first week of March 1944, allowing the fighters of the US Marine Corps' VMF-22 and VMF-223 squadrons to arrive on 13 March. Meanwhile, the indigenous people agreed to be evacuated to Guadalcanal, and some 1,147 persons were evacuated in the tank landing ships.

The airfield was used to support of the final stages of the 'Cartwheel' plan within the 'Elkton' scheme. On 17 February a small landing party was landed on Sirot island astride the North and Middle Channels, and killed 27 Japanese. A boat patrol visiting Pinepel atoll to the north killed 14 Japanese on Sau island.

The Allied losses were 13 men killed and 24 wounded (10 and 21 respectively being New Zealanders). The airfield had a runway 5,000 ft (1525 m) long by a time early in March and 6,000 ft (1830 m) long by the end of the month despite terrain and climate difficulties. On 7 March, the first air attack on Kavieng to stage though Green island arrived from Piva airfield on Bougainville. The runway was later lengthened to 7,300 ft (2225 m).

The small naval facility which was built allowed PT-boats to start operations along the coasts of New Ireland and New Britain in February. A small seaplane base was built in June and support facilities for the Naval Advance Base, Green Island, were completed in July.

Early in 1944 the New Zealand government faced a manpower crisis resulting from the maintenance demands of two divisions on overseas deployment at a time when the country was simultaneously attempting to undertake agricultural and industrial production to meet Allied requirements. To cope with this crisis the government of New Zealand felt that the only solution was the disbandment of one of the two divisions, and the decision to terminate the 3^rd Division was made after consultations with the British and US governments, which felt that the 2^nd Division’s contribution to the Italian campaign was more important than 3^rd Division’s contribution in the Pacific campaign. The 3^rd Division was therefore withdrawn to New Caledonia in June 1944 and returned to New Zealand in August. Here the division was rapidly downsized and and formally disbanded on 20 October 1944. Some 4,000 veterans of 3^rd Division were dispatched to Italy to reinforce the 2^nd Division, and the others returned to civilian employment.