When I was a kid our family frequently took summer vacations at Ocean City, New Jersey. Almost every summer one of the rituals of those trips was to go to Sunset Beach, at the southern tip of the state, near Cape May. There one could look out a short distance and see the remains of the S.S. Atlantus, a concrete ship that had beached there in 1926.
Yes, you read that correctly. A concrete ship.
The Atlantus was one of twelve ships built in 1918 as part of an emergency fleet ordered by President Wilson. The experiment was to use concrete as an alternative to steel, which was in short supply. Twenty-four had been ordered, twelve were completed, and none by the end of the war.
Atlantus, however, was used in bringing troops home from France. Afterwards, it and other ships were sold to private owners.
For more on the history of these ships, see the link: http://www.concreteships.org/
When I first saw Atlantus, I believe better than half was still visible. Today very little is still above the waves, and it is only a matter of time that the remains, a reminder of this idea from World War I, disappears completely.