QE2 was also the last oil-fired passenger steamship to cross the Atlantic in scheduled liner service until she was refitted with a modern diesel powerplant in 1986–87. She undertook regular world cruises during almost 40 years of service, and later operated predominantly as a cruise ship, sailing out of Southampton, England. QE2 had no running mate and never ran a year-round weekly transatlantic express service to New York. She did, however, continue the Cunard tradition of regular scheduled transatlantic crossings every year of her service life. QE2 was never given a Royal Mail Ship designation, instead carrying the SS and later MV or MS prefixes in official documents.