Throughout January 1944, AirSols aircraft based in the Solomon Islands and Royal Australian Air Force (RAAF) aircraft based on Kiriwina kept up a sustained air offensive against Rabaul. Under steady and relentless pressure, the Japanese air defence began to weaken, allowing a landing to be made on 15 February by New Zealand troops on the Green Islands, which lie little more than from Rabaul. On 16 and 17 February, the US Pacific Fleet's Task Force 58 attacked the main Japanese base at Truk. Most Japanese aircraft were recalled to defend Truk and 19 February saw the last significant interception of Allied aircraft over Rabaul. Meanwhile, on 13 February, General MacArthur had issued orders for the invasion of the Admiralty Islands, codenamed Operation Brewer, which was now scheduled for 1 April. Forces assigned included the 1st Cavalry Division; No. 73 Wing RAAF, providing close air support; the 592nd Engineer Boat and Shore Regiment (EBSR); the US Marines' 1st Amphibious Tractor Battalion; and US Naval Construction Battalions ("Seabees") to build the naval base—a total of 45,000 personnel. However, on 23 February 1944 three Fifth Air Force B-25 Mitchell bombers flew low over Los Negros. The airmen reported that there were no signs of enemy activity and the islands had been evacuated. Lieutenant General George Kenney, the commander of Allied Air Forces in the South West Pacific Area, went to MacArthur and proposed that the unoccupied islands be quickly taken by a small force. According to Kenney: "The General listened for a while, paced back and forth as I kept talking, nodded occasionally, then suddenly stopped and said: That will put the cork in the bottle."