The geography decided everything. Manus Island sits 387 miles from Rabaul, 694 miles from Truk, 273 miles from Kavieng, and 244 miles from Wewak - each a major Japanese strongpoint, each within striking range of an American air group based in the Admiralties. But the real prize was Seeadler Harbor, a natural anchorage large enough to hold an entire fleet and sheltered enough to do so safely. Pacific commanders had been looking at the Admiralties since 1943. When the 1st Cavalry Division took Los Negros in February 1944, the Seabees - the Navy's construction battalions - were already loading the ships that would follow. Major construction began in March while fighting still rumbled inland. The first airfield, Momote, was in use by fighter aircraft on 10 March, less than two weeks after the assault.

What the Seabees built over the next two years had no parallel in the Southwest Pacific. Four airfields eventually operated from the Admiralties. Mokerang got two 8,000-foot bomber runways. Ponam and Pityilu each hosted carrier-fighter training facilities with room for hundreds of spare aircraft. At Lombrum Point on Los Negros, crews built a seaplane base, a full ship-repair complex, and a landing-craft facility capable of servicing LCTs, LSMs, and smaller craft simultaneously. Floating drydocks were towed 8,000 miles from the United States - the largest, USS AFDB-2 and USS ABSD-4, could hold a battleship. In December 1944, USS Iowa herself sat in one being repaired. The base also included a 1,000-bed Navy hospital, a 500-bed Army evacuation hospital, 128 storage depots, 50 refrigerated warehouses, water systems producing four million gallons a day, sawmills, coral quarries, and five miles of road through what had been jungle a few months earlier.

The Mount Hood explosion remains one of the worst non-combat disasters in US Navy history. The ship was anchored with her cargo holds open for offloading when she went up. The force threw debris miles across the harbor. A column of smoke rose 7,000 feet and was visible from every ship in the anchorage. What caused it was never established - an accidental detonation of an unstable fuse, a mishandled shell, a fire that reached something that should not have burned. Every man aboard was killed. The Mindanao, working within rescue distance, had nearly a third of her crew killed or wounded. Six months later, on 22 April 1945, a Mitsubishi Zero pilot mistook USS ABSD-4 for an aircraft carrier - the drydock's sheer size deceiving him - and attacked, damaging the dock and its twin ABSD-2 in the same strike. These were the war's human moments in a place that from the air looked entirely industrial.

Most of the Manus bases were abandoned in 1946 and 1947 as the Navy drew down. Momote Airfield became Momote Airport, which still serves Manus Province today. Some facilities passed to the Royal Australian Navy, which reactivated parts of the base in 1950 as HMAS Tarangau. The rest went quiet. The floating drydocks were too big to move home economically, and so USS ABSD-2 and ABSD-4 were scuttled or left in place; their remains are still visible, massive steel boxes corroding in shallow water off Los Negros. Divers today explore the Mount Hood wreck and a scattering of Japanese ship remains around the islands. The 1st Cavalry Division Memorial on Los Negros marks where the first Americans came ashore. Standing at Seeadler Harbor now, it is nearly impossible to picture what this place was for three years - the battleships, the drydocks the size of city blocks, the hundred thousand men who passed through. Only the harbor itself remains unchanged, as big and quiet as the Navy once needed it to be.