I'm not sure about the "concrete" part, but the final Essex class carrier, USS Oriskany, was sunk off Florida to form an artificial reef, the first US naval shi

I'm not sure about the "concrete" part, but the final Essex class carrier, USS Oriskany, was sunk off Florida to form an artificial reef, the first US naval ship for which this was done, just about 20 years ago. https://en.wikipedia.org/wiki/USS_Oriskany#2004_%E2%80%93_artificial_reef https://en.wikipedia.org/wiki/USS_Oriskany#2004_%E2%80%93_ar...