English: Image of the concrete oil tanker and steamship Palo Alto on her sea trials on 10 September 1920 in Oakland, California. Palo Alto was part of a handful of concrete ships built for intended use during World War I but ultimately not completed until war's end. Palo Alto never entered service as a steamship, spending her remaining days first as an amusement attraction, a fishing pier and finally an artificial reef. Uploader's note: I contacted the NHHC regarding the copyright status of this photograph. I received an official email in reply from the NHHC stating the photograph in question was released to the public domain so long as the source and catalog number were provided wherever it may be used and I have provided such information.