There have been two ocean liners called "Queen Mary". Here are links to information about them: 

RMS Queen Mary Long Beach California

The original Queen Mary took her maiden voyage in 1936 and saw service during WWII carrying both American GIs and their new 'War Brides'. She held the legendary Blue Riband for 14 years and after a 31 year career was retired in 1967. Her final voyage was to sail all the way around Cape Horn from Southampton England to Long Beach California. She was refitted into a floating hotel and tourist attraction.

 Cunard Queen Mary 2

The Queen Mary 2, also referred to as the QM2, was launched in 2004 and at nearly 150,000 tons is the largest *ocean liner* ever built. There are two cruise ships (Oasis of the Seas & Allure of the Seas) which are larger, but they do not do transatlantic crossings.