Which Cunard ocean liner held the Blue Riband for almost 20 years after 1909?

RMS Mauretania held the Blue Riband for almost 20 years after 1909.

The Cunard liner won the record for the fastest westbound Atlantic crossing in September 1909, completing the voyage in four days, ten hours, and 51 minutes. Its average speed was about 26.06 knots, a remarkable performance for a steam turbine-powered passenger ship.

Mauretania was built by Swan Hunter at Wallsend and entered service in 1907. It was one of three closely related Cunard vessels, alongside Lusitania and Aquitania. Its turbine propulsion was a major reason for its speed and smooth running.

The ship lost the westbound record to the German liner Bremen in 1929, although it remained famous for its unusually long reign. The Blue Riband was an unofficial speed prize, not a formally administered trophy.