HMS Queen Mary was the last battlecruiser built by the Royal Navy before World War I. The sole member of her class, Queen Mary shared many features with the Lion-class battlecruisers, including her eight 13.5-inch (343 mm) guns. She was completed in 1913 and participated in the Battle of Heligoland Bight as part of the Grand Fleet in 1914. Like most of the modern British battlecruisers, she never left the North Sea during the war.