There’s also one on Guam. It was to be incorporated into Glass Breakwater in Apra Harbor but broke loose during the sinking and is intact and perpendicular to the breakwater. It was a GREAT wreck of novice wreck divers and had an air filled compartment a couple of decks down. WELL familiar with the Aptos wreck, too!
Nine McCloskey class concrete ships were partially sunk as a breakwater at Kiptopeke Virginia to protect the ferry landing for the Chesapeake Bay ferry to Little Creek. The construction of the Chesapeake Bay bridge/tunnel eliminated the ferries but the breakwater is still there.
The technology isn’t dead either .The larger luxury floating homes . Can’t call these houseboats ! Well these are built on a concrete hull that allows you a full basement even with windows at waterline level or just above or below that precious line . How do I know , well I was living on a converted coast guard boat and one was built right down the levee from me . T.B.
Anyone who wants to model one, find a copy of Shipbuilders Cyclopedia, published in 1920. There are plans there. You might find a copy in a major library’s reference section, or maybe through interlibrary loan.
The technology based on this is still in use, in places you might never expect. I was watch a BBC show called Grand Designs about custom home building, and one recent project along the Thames river featured a huge concrete barge like basement that was designed to float when the river flooded, floating the whole house safely in place.