RMS "Queen Mary 2 (also referred to as the QM2") is a transatlantic ocean liner. She is the largest and only major ocean liner built for the British Cunard Line since "Queen Elizabeth 2" in 1969, the vessel she succeeded as flagship of the Cunard Line.
"Queen Elizabeth 2" was retired after the completion of "Queen Mary 2".
The context says that the Queen Mary 2 succeeded the Queen Elizabeth 2 as flagship, but  doesn't say whether the Queen Elizabeth 2 was put out of service or not (just that it is no longer the flagship). I think the ambiguous use of the word "succeeded" confused the system.