The occupation of Emirau (20 March 1944) helped to complete the Allied noose around the Japanese base at Rabaul and saw the 4th Marine Division occupy the undefended island in the seas west of New Ireland.
The occupation of Emirau was carried out as part of Operation Cartwheel, the Allied offensive that was originally meant to end with the conquest of Rabaul on New Britain and Kavieng on New Ireland. Well before the attack on Emirau the decision had been made to bypass Rabaul, but Kavieng remained an invasion target for much longer. Even as late as 5 March General MacArthur still wanted to occupy Kavieng, as part of a general movement west in the New Guinea area. However the Naval commanders in the Pacific, including Admirals Halsey and Nimitz were opposed to the idea of an attack on Kavieng, where the Japanese had built strong defences, and instead suggested Emirau as an alternative target. The Joint Chiefs of Staff agreed with the Navy, and ordered MacArthur to carry out the operation. He passed on the task to Admiral Halsey.
Emirau is one of the St Matthias Islands. It is located around 100 miles to the north-west of Kavieng, and was thus significantly nearer to that Japanese base than any other Allied airbase, including the newly conquered bases in the Admiralty Islands.
The invasion force consisted of the newly formed 4th Marine Division, commanded by General Noble, carried on ten fast transports and protected by nine destroyers.
The attack was mounted on 20 March, only eight days after the Kavieng operation was officially cancelled. It was supported by a diversionary attack on Kavieng, in which four battleships and fifteen destroyers carried out a mock pre-invasion bombardment, supported by two small aircraft carriers.
The invasion of Emirau went without a hitch. There were no Japanese on the island, and so the marines were able to make an unopposed landing. Work began on turning the island into a powerful base. The first airfield was ready by May, and was followed by a bomber base. The smaller airfield was used to support operations over New Ireland, helping to neutralise Kavieng, while the bomber base was used against targets as far off as Truk.