Mutsu (陸奥), named after Mutsu Province, as per Japanese ship naming conventions, was the Imperial Japanese Navy's (IJN) second Nagato-class battleship. When commissioned in 1921, she and her sister-ship were the first battleships in the world with 16 inch (actually 16.1 inch, or 410 mm) guns and were considered the Japanese navy equivalents of the British Navy’s Queen Elizabeth class. At the time of their completion in 1920–21, their armament, armour and speed made them the most powerful capital ships in the world and they remained the most powerful battleships in the Imperial Japanese Navy until the completion of the Yamato class. It was not until 1937 that the US Navy became aware that their actual speed was considerably higher than the 23 knots they had previously assumed, which resulted in a redesign of the South Dakota class to provide them with a higher speed.[1]