MacArthur planned to invade the Admiralties in a division-size operation on 1 April 1944, but air reconnaissance in February 1944 indicated the islands were lightly defended. Ignoring the estimates of his intelligence staff that there were more than 4,000 Japanese troops in the islands who would likely put up stiff resistance, MacArthur decided to gamble and advance the landing to the end of February, even though all the forces earmarked for the operation would not be ready by that point. He planned to land a reconnaissance force on Los Negros and then rush in reinforcements faster than the Japanese could react.
The Admiralties operation began on 29 February with the landing of 1,000 assault troops from the 1st Cavalry Division at Hyane Harbor on the east coast of Los Negros. There were 2,000 Japanese on Los Negros; however, their commander had expected a landing on the other side of the island and placed only a few defenders at Hyane. The cavalrymen quickly captured Momote airfield and set up a defensive perimeter. Over the next days, aided by air support, they beat back piecemeal Japanese counterattacks. MacArthur poured in reinforcements, and by the morning of 4 March, the last Japanese counterattack had been defeated.
On 9 March, U.S. troops went ashore at Salami Plantation on the other side of Los Negros, and in 10 days of heavy fighting, the Americans secured the island. In the meantime, American troops landed on Manus Island west of Lorengau airfield, and with the seizure of the airfield on 18 March, the important part of the island was in American hands.
The last Japanese stronghold in the Admiralties, Pityilu Island, was captured on 31 March. Except for a few stragglers in the jungles of Manus, all of the Japanese defenders in the Admiralties had been wiped out. U.S. casualties were 330 killed and 1,189 wounded. MacArthur's gamble to advance the date of the Admiralties landing had paid off. The initial invaders had fought well even though outnumbered on 29 February, and once MacArthur could bring to bear all of the 1st Cavalry Division, the Japanese were doomed.
With the capture of the Admiralties, MacArthur could now extend his operations. Most important, at a time when the Joint Chiefs of Staff were deliberating future strategy in the Pacific war, the successful Admiralties operation helped convince them to underwrite MacArthur's ambition to liberate the Philippine Islands by an offensive along the north coast of New Guinea.
John Kennedy Ohl
The Admiralties: Operations of the 1st Cavalry Division, 29 February–18 May 1944. Washington, DC: Historical Division, U.S. War Department, 1945.; Miller, John, Jr. Cartwheel: The Reduction of Rabaul. Washington, DC: Office of the Chief of Military History, Department of the Army, 1959.; Morison, Samuel Eliot. History of United States Naval Operations in World War II. Vol. 5, The Struggle for Guadalcanal, August 1942–February 1943. Boston: Little, Brown, 1949.; Taaffe, Stephen R. MacArthur's Jungle War: The 1944 New Guinea Campaign. Lawrence: University Press of Kansas, 1998.