The battle of the Green Islands (15-20 February 1944) saw a powerful New Zealand force overwhelm the Japanese garrison of the Green Islands between New Britain and Bougainville, part of the wider campaign to isolate the Japanese bases at Rabaul and Kavieng.
The Green Islands were located between Bougainville, at the western end of the Solomon Islands and New Britain. They were 117 miles east of the Japanese base at Rabaul on New Britain and 220 miles south-east of their base at Kavieng. The Green Islands is made up of two atolls. Pinipel Island forms the northern atoll, Nissan Island is the largest of the southern group.
The group was fairly small, nine miles from north to south and five miles from east to west. The largest island, Nissan Island, is horse-shoe shaped, and curves around three sides of a large lagoon. Two islands fill the gap in the west of the lagoon - Sirot Island in the north and Barahun in the south.
In 1944 the Japanese has a barge staging base in the Green Islands.
The idea of invading the Green Islands was first suggested on 20 December 1943, after General MacArthur learnt that Admiral Nimitz wasn't planning to attack Manus in the Admiralty Islands for several months. Halsey's South Pacific staff suggested a joint attack by MacArthur's Southwest Pacific and Halsey's South Pacific commands, against Manus and the Green Islands. The idea would be to build an airfield and a PT boat base on the island, allowing Allied fighters to reach Kavieng. The capture of the islands would also cut the Japanese sea route to Buka Island, on the western shore of Bougainville. MacArthur decided to delay the attack until he was ready to attack Kavieng, but approved the plan for an attack on the Green Islands.
Early in January Admiral Halsey issued warning orders for the attack. The plan was to land on the western shores of Nissan Island, and on the night of 10-11 January four PT boats were sent to check that the passage between Hissan and Barahun Islands was deep enough for landing craft.
On 5 February command of the attack was given to Admiral Wilkinson. The landings were to be carried out by most of the 3rd New Zealand Division (General Barrowclough), along with the US 976th Antiaircraft Artillery Gun Battalion and various base units. Barrowclough had a total of 5,806 men at his disposal. They were to be transported on a mix of destroyer transports and landing craft. Air support was to come from the Solomon Islands, and two cruiser task forces were to provide naval cover. In the build-up to the attack the Fifth Air Force carried out two weeks of attacks on Kavieng to stop the Japanese from intervening.
On the night of 29-30 January a reconnaissance force of just over 300 men landed on Nissan Island to investigate the size of the garrison and the layout of the island. They reported that there were about 100 Japanese troops on the island. The troops weren't attacked, but their landing boats were fired on at one point, and later came under air attack from six fighter-bombers from Rabaul. The reconnaissance party was picked up safely on 31 January.
This raid caused a panic on the Green Islands. The existing Japanese garrison reported that it had suffered heavy losses and fled to the nearby Feni Islands. On 1 February 77 reinforcements were landed from a Japanese submarine, and on 5 February the garrison returned, giving the Japanese 102 troops. Even with these reinforcements the Japanese garrison was outnumbered by over 50 to 1!
The invasion fleet put to sea on 12-13 February and met up off Bougainville on 14 February. They were detected by a Japanese aircraft on 14 February and attacked by thirty-two aircraft on the night of 14-15 February. Twelve aircraft were shot down, and the Japanese failed to inflict any damage on the flotilla. The cruiser Saint Louis, part of the covering force, did suffer one hit.
The destroyer transports arrived at their starting point west of the main atoll at just after 6am on 15 February. The landing craft were sent into the lagoon, protected by thirty-two fighters from the Solomons. Once again the Japanese attempted to attack, this time with seventeen bombers. Once again they scored no hits.
The New Zealand landing was completed within two hours. By the end of the day all of the ships had loaded their cargos, and most then moved south. The Japanese were unable to put up any organised resistance to this overwhelming show of force. It took six days to entirely eliminate the garrison, and during the fighting the Allies lost ten New Zealanders and three American killed and 24 wounded.
One aspect of the Allied victory in the Pacific was the speed with which newly captured islands could be turned into active bases. On the Green Islands the PT base was operational by 17 February, only two days after the start of the attack. A 5,000ft long fighter airfield was ready by 4 March, within three weeks of the invasion, and a 6,000ft long bomber airfield was ready by the end of March. The Green Islands were used by a number of RNZAF squadrons for the rest of the war, although by the time the islands were captured Kavieng was no longer a threat and instead they spent most of their time operating against Rabaul.