[Llarry]

One of the major issues facing the U.S. Navy in World War II in the Pacific was the great distances that the fleet operated from U.S. shipyards. Battle damage would require a lengthy voyage of thousands of miles back to a shipyard on the U.S. west coast. This was a time-consuming task and took a combat ship out of action for an unacceptably long period of time.

As the Pacific war moved east -- closer to Japan but further from the U.S. -- the problem got worse.

The solution was a whole system of mobile ship repair facilities based on Pacific islands. A key component was a floating drydock, which would enable a ship to be raised out of the water for repairs under the waterline.

The U.S. Navy built 7 large auxiliary floating drydocks (ABSDs) in 1943-44 to address this problem. These were modular in construction, with each section being about 80 feet wide. For the largest ships (battleships or aircraft carriers), 10 sections would be joined to create an 800-foot long drydock. Outriggers at each end actually took the total length to 927 feet and the 10-section ABSD could lift up to 90,000 tons.

When necessary to relocate the dock, the dock would have to be disassembled into sections and each section would be towed to the new location, then reassembled.

The Navy discarded all these WWII-era drydocks by the turn of the century. However, new medium drydocks were built in the 1970s and 1980s specifically to accommodate nuclear submarines; these are 492 feet long with a lifting capacity of 7,800 tons. The USS Shippingport (ARDM 4) is based at New London, while USS Arco (ARDM 5) is at San Diego. These ARDMs, like the WWII drydocks, are not self-propelled and would need to be towed if relocated.