(Id. No. 3012: displacement 19,500; length 544'; beam 60'; draft 26'; speed 14 knots; complement 494; armament 4 6-inch, 2 1‑pounder, 2 machine guns)
The steamship Barbarossa, built by Blohm und Voss, Hamburg, Germany, in 1896, was operated by the North German Lloyd Line until she took refuge in Hoboken, N.J., at the outbreak of the World War.
She was seized when the U.S. entered the war 6 April 1917; damage inflicted by her crew prior to seizure was repaired; and, having received the identification number (Id. No.) 3012, she was commissioned on 3 August 1917, Cmdr. Harry L. Brinser in command. Shortly after commissioning she was renamed Mercury.
Mercury got underway for her first transatlantic troop-ferrying mission on 4 January 1918. Before the armistice on 11 November 1918, she had completed seven voyages to France, carrying over 18,000 passengers. After the armistice, she reversed the flow of troops, making eight crossings to return more than 20,000 to the United States.
After completing her last crossing as a U.S. Navy ship on 19 September 1919, she was decommissioned and was turned over to the Army Transport Service on 27 September 1919.