ABSD-4 was never meant to travel as one ship. The Mare Island Naval Shipyard in Vallejo, California built her in sections during 1942 and 1943 - nine enormous pontoons that could be towed across the Pacific folded flat, then assembled where the Navy needed them. Each section was a boxy rectangle with hinged walls that lay down under tow to reduce wind resistance. Once joined, the full dry dock stretched longer than three football fields. The inside clear width was 133 feet, 7 inches - enough to swallow a battleship. A fifteen-ton crane on rails ran along the top. Six capstans worked the lines. Four ballast compartments in each section allowed the whole structure to sink beneath a ship and then rise, lifting its cargo dripping into the air.

The convoy left California in 1944, towing the sections across 6,000 miles of open ocean. The crossing took 48 days. Assembly happened first at Espiritu Santo Naval Base in what was then the New Hebrides - now Vanuatu - where the Navy's advance base machinery was already in rhythm. By autumn 1944 ABSD-4 was at Seeadler Harbor in the Admiralty Islands, joined to Manus Naval Base and to her sister ABSD-2. The harbor had become the Navy's forward repair hub for everything MacArthur was doing in the Philippines. Ships damaged by torpedoes, naval mines, or ordinary wear needed their rudders and propellers serviced below the waterline, and there was no home port within usefully steaming distance. ABSD-4 made it possible to repair a battleship forty days' sail from a continental shipyard.

The rated lift was 90,000 tons, which put aircraft carriers, battleships, and cruisers all on the menu. USS New York - a First World War battleship still fighting in her fourth decade - was cleaned and painted in ABSD-4 in March 1945. USS Allen M. Sumner came in on January 20, 1945 for work. The drydock held her own power stations, machine shops, ballast pumps, repair shops, and mess halls for the crews that lived aboard. Everything was on the water. Everything was self-sustaining. When the repair crews broke for meals, they sat in the middle of a floating industrial complex that had not existed eighteen months earlier.

On April 27, 1945 at approximately 11:15 at night, three Nakajima B5N torpedo bombers crossed the harbor from Truk and dropped their weapons. One hit ABSD-4, striking a pontoon tank. At the time of the attack she was working on a Liberty cargo ship, a Landing Ship, Tank, and a seaplane tender - the tender itself loaded with ammunition, undergoing emergency repair. A second torpedo hit ABSD-2 in Section G shortly after. The damage was contained. Both dry docks were repaired and returned to service. Given what had happened to USS Mount Hood five months earlier in this same harbor, a detonation aboard the ammunition-laden tender would have been catastrophic. It did not come.

The war ended and ABSD-4 stayed. Reclassified AFDB-4 after the war, she was put in reserve at Seeadler Harbor off Lombrum Point and never left. Officially she was decommissioned and struck from the Navy register on April 15, 1989 - nearly half a century after the torpedo hit her pontoon. Today she rests partially submerged at Lombrum, Papua New Guinea. The outer walls still rise above the waterline, a rectangular ghost of the largest thing the Navy ever towed across the Pacific. Divers visit. Fishermen tie up. The dry dock that lifted battleships out of the sea is now a habitat for them. She has been here longer than anyone who served aboard her, and the harbor has folded her into its history the way it folded everything else - Germans, Japanese, Americans, and all the iron they left behind.