She was the first of a trio of successively larger Hamburg America ships that included SS Vaterland and SS Bismarck built by the line for transatlantic passenger service. At the time of her launch in May 1912, she was the largest passenger ship in the world superseding the White Star RMS Olympic. During World War I, the ship remained in port in Hamburg. After the war she was briefly commissioned into the United States Navy as USS Imperator and employed for returning American troops from Europe.
There is an excellent Website dedicated to Imperator. Highly recommended!