From Wikipedia: offered with a grain of salt....
Cunard Line (/ˈkjuːnɑːrd/) is a British shipping and cruise line based at Carnival House at Southampton, England, operated by Carnival UK and owned by Carnival Corporation & plc. Since 2011, Cunard and its three ships have been registered in Hamilton, Bermuda.
In 1998, Carnival Corporation purchased a controlling stake in Cunard, completing the acquisition in 1999 to become sole shareholder.[45]
Between 1989 and 1999, the company [carnival corporation] acquired Holland America Line, Windstar Cruises, Westours, Seabourn Cruise Line, Costa Cruises and Cunard Line. The name Carnival Corporation was adopted in 1993, to distinguish the parent company from its flagship cruise line subsidiary.[3]
Carnival Corporation and Carnival plc jointly own all the operating companies in the Carnival group
...the only U.S. flagged cruise ship, Pride of America [NCL] sails year round from Honolulu