During World War I and World War II, metal was a precious commodity strictly rationed for tanks, artillery, and traditional warships. Facing a catastrophic shortage of steel for merchant supply lines, the United States government funded a radical engineering gamble: floating concrete ships. While the idea of a stone boat sounds like a recipe for a submarine, basic Archimedes principles allowed these vessels to float easily as long as the weight of the water they displaced exceeded the weight of their dense concrete hulls.
Among the first generation was the SS Atlantus, a 250-foot steamer launched in 1919. Constructed with a specialized lightweight aggregate called Haydite, the Atlantus proved that concrete ships were seaworthy, though they suffered from thick hulls that reduced cargo capacity and made them sluggish to maneuver. After the armistice rendered them commercially impractical, the Atlantus was towed to Cape May, New Jersey, in 1926 to be used as a ferry wharf breakwater.
A violent storm severed her moorings, stranding her on a sandbar where her deteriorating ribcage remains a famous tourist attraction today. The concept made a dramatic comeback during WWII when Tampa-based contractor McCloskey & Company built a fleet of 24 upgraded concrete cargo ships. These WWII leviathans served vital roles in the Pacific Theater as floating supply depots, mobile repair shops, and troop transports, proving surprisingly resistant to Kamikaze strikes and magnetic mines.
After the war, nine of these McCloskey ships were lined up stern-to-bow and sunken intentionally off the coast of Virginia to form the Kiptopeke Breakwater. Though post-war steel abundance ultimately buried the concrete ship industry, these eerie marine monoliths stand as a remarkable testament to modern engineering desperation.