The SS Jeremiah O'Brien, an emergency cargo vessel of the type EC2-S-C1 better known as Liberty Ships, is one of two operative survivors of 2,751 ships, the largest fleet of single class ever built. The other is the SS John W. Brown, now in Baltimore (not operative at the time of the landmark designation). Between March 1941 and November 1945, eighteen US shipyards produced 2,751 ships. The design stressed minimum cost, rapidity of construction, and simplicity of operation. The original design and configuration have not been altered.
This is the oldest operating vessel with a diagonal, compound steam engine, with disc valve gear. Operating at a higher pressure than the oscillating-cylinder engines then used in lake steamers, this type of engine was more powerful and efficient, as well as smaller. The compound engine, built by Sulzer brothers of Winterthur, uses super-heated steam from the boilers in two stages-high and low pressure-before exhausting it into a condenser. The engine produces 650 horsepower, turning two paddle wheels.