Once the three airstrips in the Torokina Perimeter became fully functional, Mitchell moved Airsols headquarters there from Munda on New Georgia Island. The first raids by Airsols aircraft had limited success. Japanese anti-aircraft fire, especially from ships, had improved greatly since Kenney's raids, and inflicted significant damage on the raiders. The Americans developed new formations and tactics that brought about increasing attrition among the Japanese fighter arm. The Japanese Navy could no longer risk exposing its ships to the relentless air attacks, and by late January, Admiral Kusaka had banned all shipping except barges from Simpson Harbor, which removed any remaining naval threat to the Torokina beachhead. By mid-February, when the Allies captured the Green Islands, the Japanese base was no longer able to project air power to interfere. From 8 March, while the Battle for the Perimeter was beginning on Bougainville, Air Solomons bombers began flying unescorted to Rabaul. 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." Capture of the Green Islands The Joint Chiefs of Staff had determined that Rabaul was to be encircled, with invasions of the Admiralty Islands and Kavieng on the north tip of the island of New Ireland, to begin 1 April at the earliest. Admiral Halsey, anxious to maintain offensive momentum, was unwilling to leave his forces idle until then. To that end, and to provide yet another airfield close to Rabaul, Halsey ordered his amphibious forces to invade the Green Islands, a group of small coral atolls about 115 miles east of Rabaul. Reconnaissance missions determined that the native Melanesians there were well-disposed toward the Europeans, and had been alienated by the Japanese. As a result, Allied planners determined that no preliminary bombing or shelling would be carried out. On 15 February, Admiral Wilkinson landed a contingent of New Zealanders from the 3rd Division under Major General Harold E. Barrowclough. Experience gained from previous landings, coupled with detailed staff work, meant that the landings were completed with relative efficiency. In addition, interference from Japanese planes was minimal. Morison attributed 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